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."
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