How we cite our quotes:
Time and fevers burn away
Individual beauty from
Thoughtful children, and the grave
Proves the child ephemeral: (3-6)
This is the beginning of the speaker's focus on death. He notes that nothing lasts forever: children grow up and lose their beauty, and everyone dies eventually.
But in my arms til break of day
Let the living creature lie,
Mortal, guilty but to me
The entirely beautiful. (7-10)
By referring to his sleeping beloved as a "living creature," we're reminded of the fact that, one day, he will not be living. The speaker then goes on to call him "mortal;" just another reminder that we will all die some day.
On the stroke of midnight pass
Like vibrations of a bell, (21-23)
Here the speaker includes symbols of time passing – a clock and a bell – which have the effect of reminding us that time is always passing.