Like many of his other sonnets, Sonnet 73 focuses on Shakespeare's anxieties concerning old age. In the poem, the speaker evokes seasonal imagery to reflect the passage of time by using several different metaphors to compare his advanced age with that of winter. His tone is grim but resigned as he compares himself to a leafless tree; instead of sweet bird song, there is only "bare ruined choirs" (4).
Shakespeare uses a gripping metaphor in the third stanza as the speaker compares his life to that of a "glowing fire;" the connotation of his choice of adjective, "glowing" suggests that the fire is steadily dwindling. He uses the phrase "ashes of youth," that comes with an enormous sense of finality (10). His life's fire has been reduced to ashes and cannot be rekindled. As with many of Shakespeare's sonnet, the final couplet reveals the speaker's primary purpose. He encourages his loved one to appreciate their time together because he must "leave ere long" (12).