How we cite our quotes:
In me thou seest the glowing of such fire,
That on the ashes of his youth doth lie, (9-10)
If lines 5-7 put the emphasis on how destruction comes on slowly and steadily, these lines point out how beings like fire (and humans) can slowly and steadily linger on, even in the face of time's destructions. So if the previous stanza highlights the past and the destructive future, these lines put the emphasis on the present.
As the death-bed whereon it must expire,
Consumed with that which it was nourished by. (11-12)
These lines also fit into quatrain 3's pattern of emphasizing the resistance to time. This can be seen in the fact that no external force is blamed for destroying the fire; by saying that it will be "[c]onsumed with that which it was nourished by," it's as if Shakespeare's speaker is saying that the fire can perfectly well destroy itself, thank you very much. In that sense, maybe these lines could be read as a way of insulting time by denying time any credit.
This thou perceiv'st, which makes thy love more strong,
To love that well which thou must leave ere long. (13-14)
The speaker of the poem ends by finding a useful lesson in the passing of time. Even if the way we get old and die totally stinks, it has one positive aspect: it makes us truly love and cherish what (and who) we have, while we have it, because it won't be around forever. As the 20th century American poet Wallace Stevens put it in his poem "Sunday Morning", "Death is the mother of beauty." Based on Sonnet 73, we think Shakespeare just might agree.