The tone of a poem is the speaker's attitude or the position they take toward the subject of the poem. In this poem, Ben Jonson at first adopts a melancholy and regretful tone as he bids "farewell" to the child he dubs "of my right hand." This phrase recalls the descriptions in the Bible of those who sit at the right hand of God: it indicates the esteem in which the lost child was held and underscores the depth of Jonson's regret at the loss of that son.

That the speaker feels at a loss, uncertain and questioning, because of what has happened is made evident through the use of rhetorical questions. However, as the poem goes on, the speaker's tone changes: he is wondering why he should be sad that his child has, at least, escaped the miseries of "age" and other difficulties. The tone becomes contemplative as the speaker questions whether he should, in fact, "envy" the fact that this child has been released from the world. Finally, he bids the child "rest in soft peace," and his tone has become increasingly resigned to the reality of what has happened. While the child's death was painful for him, he ultimately accepts that this was the best thing for his son, who was his best work.

Before I answer that question, let's review the definition of "tone". 

Tone is a literary device that indicates the emotion the author intends to communicate in his/her work, conveyed through word choice, syntax, and figurative language. 

In "On my First Son" by Ben Jonson, the tone ranges from sadness to confusion to melancholy. He begins the poem by bidding farewell to his son and to happiness: "thou child of my right and, and joy." As he reveals, his son has died in his childhood at the age of seven, for only "seven years tho' wert lent to me." 

In line 5, Jonson's punctuation abruptly shifts to incorporate an exclamation, in which he cries out in anger and despair, "O, could I lose all father now!" With his son gone, he is no longer the father he once was, and his identity has also been affected by this loss. 

In the same line, Jonson begins to barrage himself with questions, asking himself why "man lament the state he should envy." Jonson goes on to discuss the many disadvantages of life that are avoided by an early death, implying that he finds his own sadness inappropriate to the situation and should instead feel pleased for his son. 

Finally, Jonson reverts to melancholy, noting that his son was his best piece of work, thereby tying his career into the death of his son as well. 

Ben Jonson (a contemporary of William Shakespeare) writes "On My First Son," speaking of the death of his seven year-old son.

Farewell, thou child of my right hand, and joy;
My sin was too much hope of thee, lov'd boy.

The first two lines of this twelve-line poem, express Jonson's farewell to the son he loved so much. The reference to "my right hand" might be a Biblical allusion to Christ, God's beloved son who sits on God's right-hand side. The boy was his father's "joy." Jonson admits that his sin was to expect that the boy would have a long life because:

Seven years thou wert lent to me, and I thee pay.
Exacted by the fate, on the just day.

...Jonson says he believes that for seven years, the boy was his only on loan—we assume, from heaven—and payment was taken in the form of the boy's life on the day he died (of the plague, while Jonson was away).

Oh, could I lose all father now! For why
Will man lament the state he should envy?

The first sentence in the second quatrain (four-line stanza) could mean that Jonson no longer wants to feel the pain of being a parent and losing a child, or, wishes he could be like a child to express his grief without reservations: freely and "wildly" as a child would. The rest of this segment is the author's way of wondering why he should be sad ("lament") the state his son is now in—in heaven, without pain—which is something one should envy (as per the teachings of Christianity).

To have so soon 'scaped world's and flesh's rage,
And, if no other misery, yet age?

The second part of the second quatrain explains that the boy has escaped the ravages of time: old age. And is this not a blessing for the boy? The author is trying to now comfort himself in his grief, while he may also be doubting his faith a little: he has been taught that this rest—this peace—is to be sought after according to the Christian faith.

Rest in soft peace, and asked, say here doth lie
Ben Jonson his best piece of poetry;

In these first two lines of the third quatrain, Jonson addresses his son, wishing him "soft peace" as he rests; he also hopes that all who pass the grave can know that there lies what is left of Jonson— his "best piece of poetry:" his greatest work beyond all he has ever written or done.

For whose sake, henceforth, all his vows be such,
As what he loves may never like too much.

In this last part of the third quatrain, Jonson hopes that of all the promises he makes to himself, he hopes he can fulfill the one that swears he will never again allow himself to love another as much as he loved his son, so as to avoid feeling this kind of pain again.

Ben Johnson wrote a beautiful elegy lamenting the death of his son.  “On My First Son” was also written as an epigram.  This was style of poetry begun during the ancient Greek time which a short poem, often expressing a single idea that usually has a witty ending.

The narration is first person point of view with the poet as the narrator.  Ben Jonson was a grieving father whose seven year old son died.  He talks to the child because he loves him and wants to keep him alive in his memory.  The narrator further addresses the readers as he shares his thoughts on death.  Even more, the speaker is writing for himself.  He tries to make sense of the worst thing that can happen to a parent: the death of a child.

Jonson writes as if his dead son can hear or read his words. He calls him the child of his “right hand. This represents the great value of the boy to the poet and indicates that he would have been his heir.  The idea comes from the Bible.  It indicates the reference to Jesus, who sat on the right hand of God.

Farewell, thou child of my right hand, and joy:
My sin was too much hope of thee, loved boy:
Seven yers thou'wert lent to me... 

For seven years, God loaned this beautiful child to the poet.  The use of the symbolic loan is an extended metaphor which  expresses the idea that ultimately everyone belongs to God. God allows human beings to spend time on earth; then, he takes them back to be with him. The sin of the father is visited on the son.  He loved the son so much that maybe it was too much. 

In the last half of the poem, the poet refers to a paradox.  Man cries over the loss of the loved one; however,  if the boy is returning to God,  man should envy the one who has died.  The young boy will escape the hardships of life and the despair of growing old. 

Jonson, poet and father, wants to place on the tombstone of his son that the boy was the best of all the work that the poet has every done. In addition, the poet suggests that he will never surrender himself so much to love. He will never allow himself to get so attached to anyone or anything.

The death of a child brings so many emotions.  The great loss to the parents, the unfinished life, and the unknown future—all of these aspects of the child’s death settle on the spirit of the mourners. Death is beyond the control of man. 

The ones who have lost someone look desperately to find some meaning.  Placing himself in the place of the dead one, man hopes that he too will go to a better place. Because death is inevitable it is accepted as a part of life.  The death of a child does not seem the same as an adult.  Too much is left undone. 

The two main subjects of Ben Jonson's "On My First Son" are his son and death.

His Son--

Jonson's title indicates that the poem is about his first son, and the reader of the poem realizes in the very first word, "farewell," that the son has left his father.  This could indicate perhaps that he has gone away on a trip, but as the poem progresses the reader comes to realize that the son has died. He wishes his young son to "rest in soft peace" and indicates that this child was Ben Jonson's "best piece of poetry."

Death--

This poem is about an unexpected death. Ben Jonson wrote this poem as an elegy for his oldest son Benjamin who died in 1603 at the age of seven.  Jonson attempts to reason about why his son had to die so young and can only conclude that perhaps it was because as a father he committed the "sin...of too much hope of thee," making too many grand plans for his future. 

In this moving poem, Ben Jonson writes about his son, Benjamin, who died on his seventh birthday of the plague. Thus the poem begins as you might expect with the farewell to a dead son. The speaker regrets having forgotten that the child was merely lent to him by God. He consoles himself with the thought that his son is now free of the pains of living and of growing old. In the last lines, the speaker offers an epitaph for his son, calling him "his best piece of poetry":

Rest in soft peace, and asked, say, "Here doth lie
Ben Jonson his best piece of poetry;
For whose sake henceforth all his vows be such
As what he loves may never like too much."

He concludes with a vow never again to "like too much" what he loves.

Interestingly, the central ideas of death that are presented in this poem are quite depressing. Jonson concludes that since all are to be taken from him, he must hold himself back from loving "too much" so that when the inevitable happens and death claims them, he is not so sad and grief-stricken as he was with his son. Yet at the same time his comparison of his son with a poem suggests that non of his work could ever be as wonderful as his son was to him, and indicates perhaps a new perspective on life, showing Jonson that family is more important than his work. Thus one of the central themes of this memorable poem to my mind is how we cope with death and how it changes us. Jonson seems to recommend not loving "too much" in the poem, yet at the same time his epigram suggests an emphasis on the family that clearly indicates enjoying and loving them greatly, in spite of the fear of death.

This is a very sad poem, lamenting the loss of a child. Jonson indicates in the title that it is his first son, a "lov'd boy" who was "lent" to him for seven years only, who has died. Jonson bids him farewell, describing him as his "joy" and suggesting, through the semantic field of money and lending, that he has been forced to return his boy as a kind of repayment of a debt -- possibly the debt incurred by his own sin.

However, Jonson goes on to suggest that, perhaps, he should not be sad, but should instead envy the state his boy is now in. He has escaped the "rage" of the world, not least the pain of having to grow old. He commends his child to rest in peace, and hopes that others will think of him as Jonson's best creation, his best "piece of poetry." He finally vows that for the sake of his son, he will try not to become too attached to the things he loves, suggesting that then he will be able to give them away to a better place with God.

The themes of the poem are relatively straightforward. It is a poem about parental love for a child, and especially about the grief that can be incurred when a parent loses a child. However, Jonson's love for his child does not end with the child's death. He still thinks of him, addressing this poem to him and imagining him as a great creation, "poetry," even though he is now lost to the rest of the world.

Written in 1603 at the death of his seven-year old son, Ben Jonson's style in "On My First Son" is particularly powerful for what it meant within that society to lose a male child at that age. The seventh year was the time when a girl and boy would stop wearing similar clothes (smocks, for instance) and boys would be "breeched" or wear pants ("breeches"). It was also that point when the boy's education would become more formal, leaving behind the school room or nursery where a woman would have instructed him, and entering into the world of education at the hands of a man—a tutor, teacher in private school, etc. In a sense, this is a "rite of passage." It is at this important time, with so much ahead to join father and son, Jonson's son dies.

In terms of the tone Jonson adopts, here it is much different than the manner in which he was accustomed to writing, "usually more cynical or mocking."

Looking to literary devices in the poem, here are a few I have noticed. First, an allusion is used. Allusion is when there is a reference to a famous person, place, event, etc. In this example, the allusion is to the son of God: Jesus.

...child of my right hand...

The Apostle's Creed refers to Christ who "sitteth on the right hand of God the Father Almighty..."

Additionally...

...“and joy” offers an ironic subtextual biblical allusion to Rachel’s name for her son Benjamin, which was Ben-oni, or “child of sorrow.”

There is a metaphor which compares Jonson's parenthood to a loan. (Remember that a metaphor is when two things are compared as if they are the same thing, but which only share similar characteristics.)

Seven yeeres tho' wert lent to me, and I thee pay,
Exacted by thy fate, on the just day.

Jonson's son had been lent to him for a term of seven years, like the length of a loan, and when the agreement was reached, Jonson was forced to return the boy to heaven, from where he had been granted the "loan" of the child in the first place.

There is also a paradox. A paradox is a statement that contains a kind of truth, but which at first seems self-contradictory and untrue. Jonson writes:

For why
Will man lament the state he should envie?

There is a contradiction between lamenting and envying: we might at first ask how it is possible that we should envy something which causes us grief or sorrow. In the poem's context, we understand that losing the boy causes grief, when knowing he is in heaven should make a Christian envious.

Rest in soft peace...

...is a form of imagery, giving "peace" the attribute of being "soft" (as opposed to "hard").

Last, I would suggest there is an irony in the last pair of lines with regard to Jonson's "future note-to-self" as to how he should protect his heart:

For whose sake, hence-forth, all his vowes be such,
As what he loves may never like too much.

It may be that Jonson is reminded of the temporal nature of life... that in loving things—when we "like them too much"—it is all that much more painful for us when they are taken from us, as Jonson's son was.

The first quatrain tells us that the poet, Johnson, has lost his son at seven years old. Johnson’s son died of the plague. The narrator opens the poem with an apostrophe which is when the speaker speaks directly to an imaginary person or abstract idea. Here, “Farewell,” indicates that he is speaking to his son, perhaps at his gravestone, or just to his spirit.

Beginning with “Oh, could I lose all father now” – this is ambiguous or it simply has a double or triple meaning. This could be the poet saying he’s about to emotionally lose it, grief-stricken. And/or it means that the poet is losing his child and the child is losing his father. And/or the child is speaking (or the poet imagines this) and the child says he is losing his life and escaping from the “world’s and flesh’s rage,” which is of some comfort to both father and son because the son is not physically suffering anymore.

“Here doth lie Ben Johnson his best piece of poetry.” Note that it does not say Ben Johnson’s, so here could also be a double-meaning. One meaning is that his son is his best creation; his best poetry. The second meaning is that Ben Johnson lies in the grave as well. Interpret this how you wish: part of him died when his son did, they are blood-related so physically as well as spiritually connected and Johnson (the poet/narrator) will never forget his son, his best creation. Therefore, all his poetry and all his best creation will be for his son; a lasting tribute and to keep his memory alive. “For whose sake henceforth all his vows be such.”