In Sonnet 19, the poet addresses Time and, using vivid animal imagery, comments on Time's normal effects on nature. The poet then commands Time not to age the young man and ends by boldly asserting that the poet's own creative talent will make the youth permanently young and beautiful. However uninspired the sonnet as a whole might seem, the imagery of animals is particularly vivid.
The sonnet's first seven lines address the ravages of nature that "Devouring Time" can wreak. Then, in line 8, the poet inserts the counter-statement, one line earlier than usual: "But I forbid thee one most heinous crime." The poet wants time to leave the young man's beauty untouched. Note that the word "lines" in line 10 unquestionably means wrinkles; in the previous sonnet, "lines" had at least three possible meanings.
Although the poet begs time not to ravish the young man's beauty, to leave it "untainted" as an example of perfection ("beauty's pattern") upon which all can gaze, the concluding couplet, especially line 13's beginning "Yet," underscores the poet's insecurity of what he asks for. However, nature's threatening the youth's beauty does not matter, for the poet confidently asserts that the youth will gain immortality as the subject of the sonnets. Because poetry, according to the poet, is eternal, it only stands to reason that his poetry about the young man will ensure the youth's immortality. The youth as the physical subject of the sonnets will age and eventually die, but in the sonnets themselves he will remain young and beautiful.