Quatrain 1: The persona says that his body is like a tree in fall. His hair is turning gray and falling out, and his limbs and voice tremble.
Quatrain 2: He then compares himself to twilight that waits for night to come.
Quatrain 3: Finally, his body is compared to a dying fire that is slowly smothered by the ashes it creates in burning.
Couplet: The friend continues to love him even though the friend sees that they will be separated by death soon.
Metaphorical language: body in old age=tree in fall, twilight, dying fire
tree in fall: shaking limbs of old age, birds'nest=choir loft=voice
implied metaphors: death = winter, night, dead fire
night=reflection of death
Night as the second self of death that seals all in rest.
Death as a human being with a "second self"
That time of year thou mayst in me behold
When yellow leaves, or none, or few, do hang
Upon those boughs which shake against the cold,
Bare ruined choirs, where late the sweet birds sang.
In me thou see'st the twilight of such day
As after sunset fadeth in the west;
Which by and by black night doth take away,
Death's second self, that seals up all in rest.
In me thou see'st the glowing of such fire,
That on the ashes of his youth doth lie,
As the death-bed, whereon it must expire,
Consum'd with that which it was nourish'd by.
This thou perceiv'st, which makes thy love more strong,
To love that well, which thou must leave ere long.