Can you help me understand the poem titled "Autumn," by Roy Campbell?

"Autumn," by Roy Campbell, is an extended meditation on
mutability, or earthly change. Often in poetry, mutability is lamented, but Campbell in
this poem offers it paradoxical phrase. Usually in poetry, spring and/or summer are the
seasons most often celebrated, but Campbell chooses the unusual topic of celebrating
autumn. Even more interestingly, he does not celebrate the beginning stages of autumn
but actually extols the process of loss and death that autumn brings with it. Indeed,
the poem quickly moves from discussing autumn to discussing a season even more strongly
associated with death -- winter, which the speaker calls "the paragon of art" (3), since
it

. . . kills
all forms of life and feeling
Save what is pure and will survive.
(4-5)

Winter, in other words,
strips away the non-essentials, such as the leaves of trees, leaving the trunks and
branches, the truly essential parts of trees. It is in this sense that the speaker
says,

I love
to see, when leaves depart,
The clear anatomy arrive . . .
(1-2)

Interesting here is the
word "love," which suggests not just a toleration of loss but an actual passion for it
and pleasure in it. Autumn and winter reveal the metaphorical skeleton beneath the
figurative flesh, showing those enduring parts of life that survive change. Indeed, the
poem's emphasis on survival even has a slight Darwininan ring to it: autumn and winter
kill whatever isn't tough enough to endure. All that is left is "what is pure"
(5).

In the second stanza, the speaker visualizes flocks of
geese flying, in front of the moon (itself a symbol of mutability because of its
constant changes). The geese are flying toward their winter nesting places -- flying in
flocks resembling "chains" (6), as if to suggest that their movements are instinctual,
predetermined, and irresistible. Meanwhile, the huge speading trees called "planes" (8)
have been stripped of their leaves. Once, those leaves blocked the light of the sun from
reaching the ground, but now the leaves have fallen. Meanwhile, even the dark evergreen
pine trees have thinned enough to let in "needles" (9) of light from the noon-day sun.
Notice how this second stanza reinforces all the imagery of mutability by including
references to different phases of the day. 

Stanza 3, full of varied
colors, describes still further changes, this time the transformation of olives into
oil, while stanza 4 imagines how, as dead vines are burned in the fire of a hearth, more
change -- the change of grapes into red wine -- will be reflected on the fingers of a
person holding a crystal cup.

Rather than lamenting the
coming of autumn and winter, then, this poem associates such change with purification,
transformation, celebration, and the enjoyment of shared pleasures. Spring and summer,
the poem implies, are seasons of growth, but fall and winter are seasons when the fruits
of growth are reaped and finally enjoyed.  Fall and winter should not be feared or
regretted, then; rather, they should be appreciated and savored, especially since winter
will itself give way to further change.