Shakespeare's "Sonnet 73" is primarily about aging and even the approach of death as well as their ability to make love grow. The speaker compares himself to autumn "in me behold / When yellow leaves, or none, or few, do hang / Upon those boughs." Next, the speaker compares himself to twilight, "as after sunset fadeth in the west." Finally, the speaker compares himself to dying embers on a fire "that on the ashes of his youth doth lie." The speaker's lover knows all this. "This thou perceivest, which makes thy love more strong." Therefore, love between the two is strengthened by this knowledge. Often, in Shakespeare's sonnets, there is a problem noted in the first twelve lines and a solution in the last couplet. Here, death is shown as imminent in the first twelve lines and the good consequence (that his lover's love grows stronger) in the last two. I suppose the regret of growing old, then, is lessened by the grace of great love.
Shakespeare's first 126 sonnets constitute a cycle with controlling themes that unite sections of the sonnets. He begins his sonnets with the speaker's "unqualified love for a young man whose youthful beauty is praised." He further talks about the destructive effects of time upon "youthful beauty." The sonnets then imply that the poet's beloved has either left him for another or that "the poet's affection has not been returned by the young man." At this point, sonnet 73 begins. For example, "That time of year thou mayst in me behold," implies the autumnal stage of life symbolically represented that the poet believes his beloved sees him as growing old as indicated in the following lines:
In me thou see'st the twilight of such day
As after sunset fadeth in the west;
Which by and by black night doth take away,
Death's second self, that seals up all in rest.
The poet then suggests that rather than the young man being repulsed by the decay of his old age, his lover should embrace him more fully and urgently as indicated in the following lines:
This thou perceiv'st, which makes thy love more strong,
To love that well, which thou must leave ere long.