That time of the year–Metaphor

"Bare Ruin'd choirs, where late the Sweet birds Sang. In me thou ceased the twilight of such day."

The speaker of this poem is comparing autumn to death. The leaves are falling off.  The trees are dying.  And, summer is dying away. Summer represents life and autumn comes along to end it.  He is contemplating his death to be behind that of the death of autumn. He envisions his death as the twilight of autumn. So, it is not enough to compare death to the dying of the season, but he compares it to a dark autumn evening without any light. This is taking way and he said that the reader could possibly find in  death, because the light could represent hope and there is no hope in death.