know where he is.

The speaker employs more visual imagery when he refers to love's "rosy lips and cheeks" and time's "bending sickle." We can easily see in our mind's eye a young person in love, with flushed face when they see their beloved. Likewise, the description of time, and the weapon it uses to mow down life when it reaches the end, is likewise clear. You can imagine the curved shape of the blade a reaper would use to harvest crops, just as time harvests lives.

Two central images are used in Shakespeare's Sonnet 116.

Stanza two presents the image of love as constant as a star used by navigators to determine the location of ships.  The image is an extended metaphor that makes up stanza two, and reveals love that stays constant through storms and is never shaken.

Stanza three presents the image of love's resistance to and immunity from time.  Love is not time's fool or jester or clown, and love will not yield when time and the grim reaper try to bring death to love.  Love will last until the final judgment.  What love is not--the fool--is personified to form the first image, and is followed by the image of the grim reaper.      

The enotes Study Guide on the poem explains these two stanzas as follows:

The second quatrain uses a series of metaphors to flesh out the character of proper love. Its constancy is such that it not only endures threats but actually strengthens in adversity. Its attractive power secures the beloved from wandering, and it sets a standard for all other lovers. Although conspicuous and easily identifiable, its value is inestimable. Aspects of it can be measured, and many of its properties are tangible, but it resides in another dimension, unassessable by normal instruments in space and time.

The third quatrain considers the constancy of true love under the threats of time and aging. It declares that love is unaffected by time. To begin with, love far transcends such mundane physical characteristics as size, appearance, condition, and shape. For that reason, it ignores physical changes caused by age or health. It defies time and everything in its power, including death. True love operates in the realm of eternity. Not even death can part true lovers; their union endures forever. Because love has the capacity to raise human action to this exalted state, it alone enables humans to transcend temporal limitations. Humankind becomes godlike through love.

Sonnet 116 is undoubtedly one of the most famous poems written by William Shakespeare. The poem is very much centered around the theme of love: love, to the poet, is strong, impeccable, and indestructible. We can see this straight away when reading the first two lines of the poem, which perfectly sum up this key theme:

Let me not to the marriage of true minds
Admit impediments.

Throughout this poem, Shakespeare elaborates on this theme and imagery is one techniques he uses in the process. For example, love is compared to a "star" in the poem: "It is the star to every wand'ring bark." Just like the North Star seems to be fixed in the night sky and provides guidance to people who are lost at sea, love is fixed and unchangeable, guiding people through life. Here, you can clearly see that the imagery in this poem shows the reader that the poet regards love as a constant in his life that provides him with guidance and security.

We can also see this very clearly in another image used in this poem—the image of the "tempests":

O no! it is an ever-fixed mark
That looks on tempests and is never shaken;

Shakespeare compares Love to many things, giving it many dimensions and potentialities and responsibilities and capacities. It cannot be altered, even when it comes upon changes, perhaps in those lovers, and it does not bend or cannot be removed by any circumstance. Instead, it provides something stable, "an ever-fixed mark" that can stand up to any storm without weakening. In this way, it is also like a "star" in that it presents a guide: something we can look to and count on to lead us in the right direction.

Though Time eventually takes youth away, it cannot take Love, and true Love remains constant until the end of time. These several metaphors all help to show how constant yet elastic Love is. It does not change as we change, and yet it cannot break—not real Love, at least. Since metaphor is the strongest mode of comparison (trumping simile and even personification, though Love is personified in this poem as well), it makes sense that Shakespeare would use it to describe the strongest mode of feeling. There can be no impediments, the narrator states, to Love, and metaphors are likewise powerful.

William Shakespeare uses comparisons – particularly similes and metaphors – in various ways in Sonnet 116 (“Let me not to the marriage of true minds”). Those ways include the following:

• In line 1, the speaker uses a metaphor to compare the union of two minds or souls to a “marriage.” This word implies a long-term mutual commitment sanctified by God and perceived as holy and immutable. Such a union merits social respect and speaks well of the two parties involved.
• In line 5, the speaker uses a metaphor to describe true love as “an ever-fixèd mark,” meaning a landmark, especially one visible from sea.  This phrase calls attention to the mutability of the world, which requires the existence of firm landmarks if we hope to find a sure path as we navigate through life.
• In line 7, another metaphor compares true love to a distant star, especially (perhaps) the North Star, which is extremely lofty in its position abovc the world (as true love transcends all merely worldly things) and which, like the landmark already mentioned, can be used to help us navigate and find our ways through life.
• In line 10, another metaphor implicitly compares Time to a harvester, perhaps the proverbial “grim reaper,” suggesting that true love escapes the ravages of time:

Love’s not Time’s fool, though rosy lips and cheeks
Within his bending sickle’s compass come . . . (9-10)

Interestingly, metaphors are common in this poem, but similes are not. It is as if the speaker tries to imply the strongest possible links – even identification – between the various objects he compares.