yellow. This is autumn, a time of change—and also the beginnings of death in nature. The speaker is facing a season of change. The imagery at the end of this stanza sets up the choice he makes:

And looked down one as far as I could
To where it bent in the undergrowth

The initial path he examines has an uncertain path. Covered by "undergrowth," the road turns and he can't tell where that destination will end.

So he takes the other road, which doesn't exactly support the more difficult choice. Check out the imagery when the speaker initially makes the choice regarding which path he will take:

Then took the other, as just as fair,
And having perhaps the better claim,
Because it was grassy and wanted wear;
Though as for that the passing there
Had worn them really about the same,

The path he chooses is "fair," covered in grass (not rocks and boulders) and is inviting. Also important is that the two paths are worn equally. This is not the less traveled road. It is as equally traveled as the road he doesn't choose.

The speaker reinforces this idea with the imagery at the beginning of the third stanza:

And both that morning equally lay
In leaves no step had trodden black.

Neither road shows the clearly less-traveled path. Both are covered in leaves which have not been disturbed.

Also notice how the language shifts to reflect an almost archaic and fanciful tone at the beginning of the final stanza:

I shall be telling this with a sigh
Somewhere ages and ages hence:

"Shall," "hence," and "ages and ages" has the same feel as "Once upon a time." The speaker slips into this almost fanciful language to remind the readers of the fantasy he has created about the "difficulty" of the path he has chosen.

The imagery and language Frost uses conveys a message that people often want to retell the glories of their most difficult choices and paths, but they fail (intentionally or unintentionally) the recall the accuracy in details of those choices. Also important is the fact that the title is "The Road Not Taken," not "The Hard Road I Took." The speaker tells "with a sigh" of his "road less traveled by," but all the while he is actually remembering "The Road Not Taken."

The previous educators have thoroughly outlined most of the poetic devices in the poem, but none have yet written about Frost's choice of meter.

Frost employs an "abaab" rhyme scheme. This is a cinquain, or a poem or stanza composed of five lines. Cinquains are seen in limericks, for example, though those poems employ a different rhyme scheme.

As one previous educator mentioned, the road is a metaphor for the different "paths" one may take in life. Both were "worn," meaning that many others had taken the same path, or made a similar choice in life. 

Frost's choice of "morning" and autumn are also metaphoric. One's autumn years indicate late adulthood. "Morning" indicates a new beginning. Even late in life, we get chances or opportunities to make life-changing choices. 

Sound devices are techniques which lend a sense of rhythm to a poem. They include end rhymes, internal rhymes, meter, alliteration, assonance, and consonance, all of which cause emphasis to fall on certain words, syllables, or sounds in a poems.

"The Road Not Taken" seems perfectly simple and almost like casually spoken speech, but it is carefully structured. For example, it follows an ABAAB pattern of end rhymes. In the first stanza, for example, "wood," "stood," and "could" are the "A" rhymes, while "both" and "growth" are the "B" rhymes.

Second, the stress falls on the second syllable in each foot or pair of beats, but since each line has only nine syllables, the stress ends up falling on the rhyme at the end of the line, adding even more emphasis to it.

The poem also uses alliteration, or putting words beginning with the same consonant in close proximity, for example, in "wanted wear," and "lay/In leaves."

Figurative language is when words are used to convey an idea beyond their literal meaning, usually by way of comparison. Figurative language is fundamentally metaphorical, allowing us to understand one thing in terms of another kind of thing. In "The Road Not Taken," Frost uses an extended metaphor in which a fork in the road represents the decisions one makes on the path of life.

Indeed, the fork in the road is the poem's central metaphor. Just as a traveler walking in the woods must choose which paths to take, people must make choices in life, and these choices continually lead to further choices.

The poem further develops this metaphor by stressing that once a path is followed, it is impossible to go back to the original path. Having made up his mind to take the second road, the speaker says,

Oh, I kept the first for another day!
Yet knowing how way leads on to way,
I doubted if I should ever come back.

That is, the speaker will have taken so many different routes that he cannot return to the original fork in the road. This aspect of the metaphor suggests the linearity of life. Just as a traveler will tend to continue onward in their journey, people cannot repeat the past or go back and change the decisions they have made in their lives.

First, concerning Frost's "The Road Not Taken," the speaker doesn't "have" literary devices, he "uses" literary devices.

And the central literary device he uses is extended metaphor.  In literature, roads and journeys often symbolize the roads or journeys of life, and the speaker's use here is no exception.  The road the speaker chooses to travel is metaphorically compared to the road he takes in life, and the road he chooses not to take is metaphorically compared to the road he does not take in life. 

That said, the road the speaker chooses not to take is really the center of the poem itself.  The poem is about regrets concerning missed opportunities.  More specifically, the poem is about the speaker's obsession with missed opportunities.  He is indecisive and regrets not being able to take both roads, even though doing so is impossible. 

The speaker will tell the story years later, as a regret, a "sigh," perhaps a chuckle.  He doesn't know what difference his choice of road will make, and the roads are pretty much the same, by his own admission:

Though as for that [there being a difference between the two roads], the passing there

Had worn them really about the same,...

But in the poem's present he can see himself, having obsessed over the difference for years, telling listeners that a great difference existed.

Concerning other literary devices, the enotes Study Guide on the poem says the following:

Frost composed this poem in four five-line stanzas with only two end rhymes in each stanza (abaab). The flexible iambic meter has four strong beats to the line. Of the technical achievements in “The Road Not Taken,” one in particular shows Frost's skill at enforcing meaning through form. The poem ends:

Two roads diverged in a wood, and I—

I took the one less traveled by,

And that has made all the difference.

The indecision of the speaker—his divided state of mind—is heightened by the repetition of “I,” split by the line division and emphasized by the rhyme and pause. It is an effect possible only in a rhymed and metrical poem—and thus a good argument for the continuing viability of traditional forms.

Diction is the style of speaking or writing and the choice of words used. Diction can refer to whether a poem is formal, informal, colloquial, or uses slang. Formal diction tends to be deemed more serious, but the Romantic poets tried to use more informal diction to make serious statements about poetry and life. The diction (style) of a poet might also have to do with his/her era or his/her particular subject matter and tone. 

The tone and the poetic quality of this poem are very serious. But Frost does use simple or informal vocabulary to illustrate the simplicity of the theme: making difficult choices. He uses a formal style but with an informal landscape of the woods from which to derive the metaphor. 

Stylistically and poetically, the poem is formal. This poem was written in 1916 when other poets were abandoning classic poetic words like "hence" and avoiding classic techniques like subject/verb inversion: "long I stood." Frost uses a balance of a classic-sounding style with simplistic and informal word choices. So, it is serious but accessible. 

Some poets use "natural diction" which comes closer to natural speech. Here, Frost uses "poetic diction," that which more traditionally resembles poetic speech. Although the poem is about a natural and common event in life, Frost uses poetic speech to underscore the drama of his choice. For example, if he had opted for more natural diction in the last two lines, he might have said, "I will be saying this with a sigh / Sometime in the future." 

Word choices are informal but descriptive. The style is formal and serious. Frost really stresses the seriousness in the final lines when he repeats the pronoun "I": 

Two roads diverged in a wood, and I -
I took the one less traveled by, 
And that has made all the difference. 

He repeats the "I" to illustrate his hesitation and uncertainty, even in old age, that he will always be unsure if he had taken the road less traveled. 

The word sigh can be considered an example of onomatopoeia because, in some ways, it does sound like what it describes. An actual sigh often begins abruptly and then lasts until all the breath is pushed from one's lungs. The word sigh is similar: it begins with a concrete and definite sound and then ends when one stops expelling air.

One might classify the narrator's description of the second road, that it has "the better claim" upon his attentions, as an example of personification. The road is grassy and fair, and so it seems to present a better option to the narrator, but to suggest that it has a "claim" makes it sound as though it has a will or the intention to draw the narrator's attention to itself.

Finally, I think one can argue that the comparison of the two roads in the second stanza—that the narrator looks at the second road, which appears to "as just as fair" as the first—is a simile. It's true that two roads in general may not seem to be terribly dissimilar, but the narrator is, in fact, describing their differences as well as their similarities. One road bends away into the undergrowth up ahead, and the other is as fair as the first, though it may present a more attractive option because of its grassiness. In comparing and contrasting the roads, it makes sense that the narrator would use a simile, and the words "as just as fair" fit the bill.

This is a tricky question, because many of the elements that you ask about are not actually in the poem. 

There is no onomatopoeia in this poem. Onomatopoeia is when the sound of a word imitates the actual sound to which it refers. An example of onomatopoeia might be "bang" or "achoo!" The word "bang" sounds like the sound of a bang, while the word "achoo" sounds like a sneeze. 

You may have incorrectly identified sigh as onomatopoeia in this poem. The word "sigh" is generally not considered to be onomatopoeia because the sound of the word does not resemble the actual sound of a sigh. 

Personification occurs in the line "because it was grassy and wanted wear." Personification is basically ascribing human traits to an inanimate object, idea, or animal. In this case the speaker is describing the road as having a desire, which is a trait normally attributed to people.

There are no similes in this poem. A simile compares two very different things by using the words "as" or "like". An example of a simile might be, "My cousin is as cheerful as a morning bird." Two dissimilar things - my cousin and the morning bird - are compared using the word "as". 

You might spot the phrase "as just as fair" in this poem and wonder if this could qualify as a simile. Because you are comparing two very similar things, in this case two roads, this does not constitute a simile.

The four stanzas of “The Road Not Taken” by Robert Frost revolve around the central extended metaphor of a fork in the road, which is compared to the choices that one must make in life. The speaker is a traveler in a “yellow wood,” and when he comes to that fork, he peers down one of the roads “as far as I could” to help him decide which road to take. At first the speaker states that the road he ends up choosing is “grassy and wanted wear.” One could interpret this part of the poem by saying that the speaker, by choosing the grassier, less traveled way, chooses the non-conventional way of life, refusing to follow the ways of others. The popular interpretation focuses on this as the central theme of the poem—that one must be the trailblazer and not just follow what other people do.

But we have to read closely and notice the interesting twist at the end of the second stanza, which seems to negate this interpretation.

Though as for that, the passing there
Had worn them really about the same.

Thus, the two roads don’t seem to be that different from each other after all. Frost uses some alliteration in this stanza, emphasizing the road “was grassy and wanted wear.” The use of those “w’s” gives the poems a hypnotic and soft quality that allows us to move through the lines quickly as do the “th” sounds in “though as for that, the passing there” and the lulling “l’s” in “lay” and “leaves”:

And both that morning equally lay
In leaves no step had trodden black.

This lovely flow of sounds without any harsh alliteration to break up the lines emphasizes the idea that these roads are indistinguishable; nothing makes one road stand out more than the other. There is no marking from the harsh “black” “step.” (Notice the way the “b” and “ck” sounds in “black” and the “st” and “p” sounds in “step” break up the earlier softer alliteration.) So how do you choose which road to take?

This is the central theme of the poem—that when we come to a crossroads in our life, we must make a significant decision that will alter our lives forever. But, again, how do we choose? Although the speaker says that he can always come back at some point in the future and take that other path, “the road not taken,” he admits that he probably won’t ever come back to this particular fork in the road again.

Yet knowing how way leads on to way,
I doubted if I should ever come back.

Once you travel down a path, you tend to keep going rather than turn around and start over. Or, if you do try and start over, you are not the same person that you were when you first stared at that fork in the road. You can’t “come back.”

The speaker then performs another final shift at the end. He suddenly shifts forward in time, imagining himself in the future, looking back at this momentous decision.

I shall be telling this with a sigh
Somewhere ages and ages hence.
I took the one less traveled by,
And that has made all the difference.

When the speaker sees himself in the future, reflecting on this moment, he revises the story, returning to his first interpretation, that the path he chose was the “less traveled” one. He wants to see himself in this trailblazing way, as one who did not follow others but instead did things his own way. And yet, what do we make of that line, that his choice “has made all the difference.” What kind of difference? Did he make the right choice? Or is he looking back with regret? And how do we interpret the title of the poem? Is “The Road Not Taken” referring to the road that he actually took (but wasn’t “taken” by others)? Or is the speaker focusing on that road that he didn’t take, wondering how his life would be different if he took that other road? And here’s yet another interpretation: is this a poem regretting not so much choosing this path or that path, but the fact that we must choose at all? Wouldn’t we rather have both roads, as is stated in the first stanza:

And sorry I could not travel both
And be one traveler…

The final alliteration in the last stanza introduces the only harsh alliteration, with the repetition of the “s” sound in “sigh” and “somewhere.”

I shall be telling this with a sigh
Somewhere ages and ages hence

This hissing quality to these words introduces a bitterness to this memory—the harshness of the idea that we cannot have both roads. We cannot enjoy all the world has to offer. We must travel this one life, one choice at a time.

The biggest metaphor in the poem is undoubtedly the roads as literal and figurative paths in life. Each path will lead to another, just as each decision we make in our lives leads to another, and eventually we end up far from where we started due to the long chain of events that follows each choice we make. The general mood created by the speaker's famous sigh in line 16 is sentimental and even nostalgic, which adds to the serious mood of the poem. 

The alliteration in the poem contributes to the lyrical quality of the poem. One of the only instances of Frost's alliteration is in line eight when the speaker says the path "wanted wear." However, instances of repeated consonants near each other also contribute to the poem's lyrical quality, like in line one with "yellow wood." 

You ask why Frost uses "literary techniques to reveal journeys."  You don't ask how he does it or what the results of what he does are, so I will specifically answer the why.  

First, why does he use literary techniques to reveal journeys?  Because that's what poets do.  Metaphor, in a broad sense, is at the heart of most writing, but especially poetry.  Human beings tend to think in metaphorical terms.  Comparison is one basis of our knowledge and how we learn.  Metaphor in poetry allows readers to feel a sense of discovery as we "decode" the metaphor, and readers love to think we are making discoveries. 

Using metaphors gives layers to the ideas poets express.  Metaphors have two parts:  tenor and vehicle.  The tenor is the idea the poet wants to communicate (decisions made in life, for Frost, here), and the vehicle is whatever is used to help explain the tenor (the fork in the road, for Frost).  Frost uses metaphor because it works.  It's a better way to explain.

There are other literary techniques used here, of course, but metaphor dominates the poem.

I think that you want to analyze the language Frost uses in the poem that helps to convey that freedom and the act of choice can represent its own journey or voyage.  Note in the first stanza, the use of terms such as "traveller" and "travel."  The roads themselves might not represent this journey, as much as the analysis of which path to take. In this instance, the voyage is the process and not the product.  The next two stanzas go through the criteria that helped the speaker make the choice of which one of the two paths to take.  Again, this might reflect how the real journey is the choices made upon them and not anything else.  Freedom and choice are journeys, voyages into the hearts and minds of those who have to make such decisions, and Frost might be trying to explain this through the language selected.

In regards to the poem's structure, look first at its rhyme scheme and meter (scansion).  The rhyme scheme reflects an ABAAB, CDCCD, EFEEF, GHGGH pattern.  While the rhyme is very structured, the meter is not so strict.  It is mostly iambic tetrameter, meaning that it has four feet per line (tetrameter), and mainly an unstressed/stressed beat (iambic).  It varies slightly from this meter, but if a reader listens to someone read the poem aloud, he/she will hear the stress on the syllables.

In regards to specific devices in the stanzas, here are several examples.

Stanza One: While this stanza does not contain any significant sound devices such as you mentioned, it does rely strongly on inversion (unusual word order).  Notice lines 2 and 3.

Stanza Two: Assonance does play a key part in this stanza.  Frost uses many short As in words such as grassy, passing, as, having, and had. Similarly, "wanted wear" in line 8 is alliteration.

Stanza Three: The rhyme of stanza three also represents "A" assonance with an alternation between long and short As.

Stanza Four: There is "ll" and "g" consonance in this stanza.  See shall, telling, and all, and repetition of ages along with diverged.

Since your question focuses on sound devices, a good argument can be made that Frost chose his sounds, words, structure, and rhyme to represent a more conversational tone.  His poem certainly appeals to the common man, someone who has to make an important decision at some point in his life.

The whole poem is metaphorical. The two roads that diverge are a metaphor for the possible life paths that a person can take. In much the same way that the author could not travel both roads, a person cannot take two life paths. And in much the same way that we might want to explore a particular option we have bypassed, later on our present journey takes us down roads that make it not possible to do so:

"I saved the first for another day
Yet knowing how way leads on to way
I doubted if I should ever come back."

There is imagery in stanza 1: "Two roads diverged in a yellow wood," and again in stanza 3 where he paints a picture of roads in the early morning littered with leaves "that no step had trodden black."

There is overstatement in stanza 4 when he says "ages and ages hence,” since the author could not be that old.

There is antithesis--the presentation of a contrasting idea to show a balance--when he says in lines 1 and 2 that two roads diverged but he is sorry he could not travel both. There is also antithesis in stanza 2 when he says the second path had perhaps the better claim as it was grassy and wanted wear, and then he comes later in the stanza to say that both paths had been worn "really about the same.”

Once one has made a full reading of the poem, it is clear that the primary poetic technique employed throughout the poem is the extended metaphor. An extended metaphor is an analogy that runs throughout the poem and in which the poet makes a comparison to the subject in the poem to something else.

The metaphor in this poem relates to the idea that life is seen as a journey. Frost compares his choice about the two roads he faces in the woods to the choices we make in life. Once a specific choice has been made, there is no turning back and one can only ponder about what the result would have been if one had made an alternative choice, just as the speaker does in the poem. 

In terms of the question regarding the concept of discovery, it is quite clear through the extended metaphor that on ones journey through life, one is faced with many alternatives. It is a matter of choice, and in our poem the speaker chose the road 'less travelled by' which, to him, has 'made all the difference.' We are not quite clear whether the difference was good or bad, since the speaker does not tell us.

Thus poet leaves us with a very clever conundrum in the end, forcing us to wonder and make a choice ourselves about whether the speaker's choice had been a good one or not. In this, he once again emphasises the central theme of the poem: that our journey of discovery is about making choices. The answer to the conundrum has encouraged much debate over the years, one which is still ongoing.

In the first stanza, the poet uses repetition. The poet repeats 'and' at the beginning of three consecutive lines, from line three to line four. 'And' is repeated in lines 7, 11 and in the last line. The repetition reflects the speaker's uncertainty, which is especially accentuated in this instance. In the other lines 'and' is used more as a connective but reminds the reader of its use in lines three to four, which once again, denotes its importance.

The rhyme scheme follows the same pattern throughout the poem: abaab; cdccd; efeef; ghggh. This binds the poem and underscores the extended metaphor and the central theme of the poem. Furthermore, each line consists of nine syllables (except line 15, which has ten) which gives the poem a regular, flowing and steady rhythm. Because this rhythm is broken only once in line fifteen, it gives the poem continuity, affirming once again the continuation of a journey. 

The break in rhythm in line fifteen creates a pause, emphasising not only the  speaker's uncertainty - further informed by the word 'doubted' - but also tells us that the speaker realises that once the choice has been made, there is little chance of coming back.  

It has become a common coined phrase - "The Road Not Taken" - as has "the one (road) less traveled" and Robert Frost's poem deals with the decision-making process and the consequences of any decision once made. The title suggests that the speaker feels wistful about what may have lay ahead had he chosen the other where he had "looked down... as far as I could To where it bent in the undergrowth."

The speaker is worried about what opportunities he may have missed but at the same time did not want to take the easy way out; hence, he considered one and "Then took the other."

The theme of choices and consequences continues to bother the speaker who is a little confused and is concerned that , after his initial analysis "the passing there Had worn them really about the same," indicating that, even though he has just made a decision, he is already potentially regretting it.

After his acceptance of his decision " I kept the first for another day!" he basically acknowledges that having taken the other path, there will be opportunities on that route that may lead him in a completely different direction - "Yet knowing how way leads on to way I doubted if I should ever come back." There is an acceptance in that but still a hint of regret as in later years he "shall be telling this with a sigh."

The speaker is resigned to the fact that there is no right or wrong decision in fact although the particular decision made will definitely make "all the difference." The reader is left to contemplate whether the speaker did make the best choice!

Robert Frost denied that his poem "The Road Not Taken" had the deep, existential meaning that many have wished to give it, insisting that he had written his verse in order to "fool his way around" in a teasing reflection on his friend Edward Thomas, with whom he took walks frequently. On such strolls, Thomas would castigate himself for not having selected another path no matter which way they went. And, yet, despite Thomas's own characterization of the poem, "The Road Not Taken" as "the fun of the thing," it became very popular as a poem of deep meaning. 

Interestingly, Frost himself contributed to the idea that there can, indeed, be a deeper significance clothed in metaphor in his poem as he wrote in one of his notebooks,

Nothing ever so sincere
That unless it's out of sheer
Mischief and a little queer [odd]
It won't prove a bore to hear.

So, the concept of "many a word of truth is spoken in jest" may, indeed, exist in Frost's poem about two roads. Alluding to these thoughts of Frost's own, the reader can, then, reasonably interpret the ambivalence in choice of paths that the persona of "The Road Not Taken" experiences as a metaphor for the indecisiveness of man that often proves tragic or, in the very least, disconcerting. And, of course, the "road" can be perceived as the "road" of life; that is, the many choices, or paths of action in a person's life.

The lightly satiric tone of Frost's line "I shall be telling this with a sigh" in "The Road Not Taken" suggests the theme of indecisiveness. That is, the reluctance of someone to make decisions lest the person make the wrong ones. Of course, the ultimate problem is that the ambiguity and lack of decision sometimes leads to more negative results than anything else. 

In order to indicate this thematic indecision, Frost employs certain literary techniques:

• Repetition

    In the first stanza, the word And is repeated at the front of each line, indicating hesitation; for, the use of the same word "And" holds back the forward movement.
    In the second stanza, the word as is repeated twice in the first line, and then in the fourth line in such a manner that it pulls back the phrases following this word:

Then took the other, as just as fair,...
Because it was grassy and wanted [here "wanted" means "lacked"] wear;
Though as for that the passing there

    The word "same" and its idea in "just as fair" is repeated in this second stanza, as well.

• Circuitous language

    In the second stanza there is no forward movement of thought as the speaker deliberates on the paths circling in thought with such words as "perhaps," "because," "though," and "really about the same."

• Conditional words

    Such words as "knowing how way leads on to way," "doubted," and "if ever I should" are used in the third stanza.

• Irregular meter in lines

    While most of the poem is written in iambs [unstressed syllable followed by a stressed syllable (ta DUM), which is the normal pattern of spoken English, there is a slowing in each line with the insertion of an anapest [unstressed syllable, then another unstressed, followed by a stressed]. This slowing is suggestive of delay, hesitation, and indecision. 

• Symbolism

    For Robert Frost trees serve as borders. His first line reads that there is "a yellow wood." The addition of the word "yellow" which often connotes danger and being overly analytical and the woods and later "undergrowth" suggest lack of movement, something that accompanies indecision. 
    In the third stanza, Frost writes that two paths "diverged in a woods," suggesting again the border and end of movement. Also, in the third stanza, the color black appears. This use of the black can symbolize negative conditions, too.  

What change is it that you are refering to in this great poem? Do you mean the way in which the final stanza suddenly projects the speaker into his own imagined future when he will look back and think of the choice he made? I will assume this is the case, but please respond to my answer if I have not understood your question correctly.

Let us focus on the final stanza and its content:

I shall be telling this with a sigh
Somewhere ages and ages hence:
Two roads diverged in a wood, and I--
I took the one less travelled by,
And that has made all the difference.

I think one of the major techniques that is used in this final stanza is that of repetition. Note the way in which the third line is basically a copy of the first line of the entire poem. This of course helps to conclude the poem but also leads towards the way in which this is a momentous decision that the speaker has to make. It helps us focus on the way in which this one decision has "made all the difference" in terms of the future of the speaker's life. Choosing the path "less travelled" has resulted in one specific kind of future, whereas, it is suggested, if he had taken the other path, he would have had a different kind of future.

The use of the word "sigh" in this last stanza greatly interests me. It seems to point towards a kind of introspective rumination about the kind of life that the speaker would have experienced had he selected the other path. The title of the poem, focusing on "The Road Not Taken," likewise reinforces this view. To me, this captures the way in which we can often find ourselves haunted by the decisions we have taken in our lives and the way that they have resulted in our present realities. Major life decisions like not marrying or marrying somebody, moving to a different city to take a job or refusing such an opportunity could radically impact our lives, just like the two paths that lie before the speaker. Perhaps the final stanza indicates a change of tone to a more introspective, meditative wondering about different possible futures that the speaker could have enjoyed, but at the same time sadness regarding the way that such alternative futures have been irrevocably lost with the choice of one path over another.