The main theme of the sonnet is love or longing for the presence of one physically absent. The sonnet begins with a description of the hard physical labor of travelling during the day. It describes how tired the narrator is after a day of travel. However, the narrator is unable to sleep because he makes a second journey at night, not with his body but with his mind. In his mind, he travels to see his beloved and that image he encounters in his mental journey illuminates the night and turns exhaustion to joy.

This narrative leads to a second theme of a mind/body dichotomy, in which physical separation and its sadness are overcome by the ability of the imagination to make present things that are physically absent. In this way, love can triumph over separation.

The theme of Shakespeare's sonnet 27 is that the speaker's body and mind work equally hard. First, the speaker's body by day does the physical hard work of traveling, which the narrator says leads to, "limbs with travel tired."

But the mind works just as hard at night. Behind his closed eyes, the speaker's imagination flourishes. The speaker's thoughts now travel on a "pilgrimage" to the beloved. The beloved dangles in the traveler's thoughts like a jewel against the "ghastly night." This sight makes the night beautiful.

In this light-hearted sonnet, Shakespeare ends on a couplet in which the narrator complains he can get no rest between the work his limbs do by day and his mind by night.

An important theme that emerges is that imaginative work is just as hard as physical labor. An active mind, full of thoughts and images, gets tired.

Sonnet 27 depicts a person who goes to bed after an exhausting day of travel. Despite his exhaustion, he is unable to sleep, as he imagines a person far away whom they long to see. This would be agonizing, as he desperately craves sleep, and is saddened by the fact that he cannot be with the one he longs for.

But his lack of sleep is more than compensated for when he imagines the image of his friend in the night. His "soul's imaginary sight" presents the image "like a jewel hung in ghastly night." This image, though imaginary, makes the night beautiful, though he still longs to be with his friend.

Two prominent themes in this sonnet are separation and longing—he is overcome by a pain created by a powerful desire to be with his beloved. Another is imagination itself, a theme he pursues in many of his dramas. He is able to make the night pleasant only because the image of the one he loves appears in his mind's eye. The theme of sleep is present in Sonnet 27 as well. This appears in several of his other sonnets as well as some of his comedies (A Midsummer Night's Dream, for example) and his tragedies (Macbeth).

A very meditative poem, Sonnet 27 discusses the theme of reminiscense and seperation. The poem depicts the narrative who is wise awake and deep in his thoughts during the night. The worries and thoughts that are preventing him from falling asleep are from seperation from his beloved one. The nostalgia and the feeling of missing someone is clearly portrayed throughout the sonnet.