The Wild Swans at Coole
How we cite our quotes:
I saw, before I had well finished,
All suddenly mount
And scatter wheeling in great broken rings (9-11)
The speaker's inability to finish what he is doing, and the swans' sudden departure ("suddenly mount," "scatter"), point to the suddenness of death and the abandonment that goes with it.
All's changed since I, hearing at twilight,
The first time on this shore,
The bell-beat of their wings above my head,
Trod with a lighter tread. (15-18)
The speaker used to tread "with a lighter tread," but doesn't anymore. That carefree part of his life is over, dead and gone. It is not totally ridiculous to think of life as a series of deaths—things change ("all's changed"), people enter and leave our lives, etc.
[…] when I awake some day
To find they have flown away? (29-30)
The swans' disappearance is a kind of death. In a way, the speaker imagines the swans leaving him because it is easier to accept their "death" than to think about the undeniable truth that he, too, (and other people he knows) will die someday.