How has Shelley portrayed the West Wind as a symbol of Life and Death?

Shelley composed  the "Ode to the West Wind" while in
Florence, Italy in the year 1819. It was published in the year 1820. The gist of the
poem is that Shelley considers himself as a poet prophet campaigning for reform and
revolution using the "wild west wind" to destroy everything that is old and defunct and
plant new and progressive, liberal and democratic ideals in its stead. The poem
describes a storm arising in the autumn season in the Mediterranean Sea and being driven
towards the land by 'the west
wind.'

In Canto
1, Shelley addresses the west wind directly as
the "breath of autumn's being" and the
sight of it driving away all the fallen leaves is  compared to a magician or an
enchanter driving  away all the evil spirits. At the same time it carries with it the
fallen seeds to deposit them in a different place where they will blossom in the spring
season after being safely preserved during the cold winter season. The west wind is thus
both 'destroyer' and 'preserver':

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Wild Spirit, which art
moving everywhere;

Destroyer and preserver;
hear, oh, hear!

In Canto
2 Shelley vividly describes the meteorological process of the
gathering storm in the distant horizon of the Mediterranean
Sea.

In the first stanza Shelley compares the storm clouds
which are being formed at the horizon ("tangled boughs of Heaven and Ocean") and being
driven inland by the west wind to decaying leaves shed by the trees during
autumn.

In the next two stanzas, the storm clouds are
compared to  "angels" which carry the rain inland. They announce their arrival by fiery
flashes of dazzling lightning which reach up into the sky from the ocean at the horizon.
The flashes of lightning are compared to the bright hair of the maenad (the maenad is a
frenzied  spirit which attends on the Greek God
Dionysus.

In Canto 3
Shelley  describes the action of the west wind on the
Mediterranean Sea and on the Atlantic Ocean. The west wind announces to the
Mediterranean Sea that summer is over and autumn has arrived. The clear view on a bright
summer day of the under water palaces and towers in Baiae's Bay off the coast of Naples
near the island made up of volcanic rock is disturbed by the west wind which blows
across it. Similarly the west wind creates deep valleys as it blows across the level
Atlantic Ocean and reminds  the underwater vegetation deep below  that it is autumn and
that they too must disintegrate like the vegetation on the earth
above.

Canto
4 is an
earnest plea by Shelley to the west wind to infuse him with its raw power and liberate
him from the bout of depression which has temporarily overwhelmed him - most probably
caused by the death of his son William in 1819. Shelley tells the west wind that when he
was a boy he was also as "uncontrollable" as the west wind is now, and he would have
easily matched the west wind in its speed. But now, he is depressed and weighed down by
the cares and anxieties of life and prays to the west wind to liberate him. He pleads
with the west wind that just like how it lifts up the leaves on the earth and the clouds
on the sky and the waves on the sea it should free him also from the "thorns of life" on
which he has fallen.

In Canto
5, Shelley the poet directly and explicitly asks the west wind
to make him an instrument and tool of political and moral change: "make me thy lyre" and
"drive my dead thoughts over the universe":

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Drive my dead thoughts
over the universe

Like withered leaves to
quicken a new birth!

The
poem ends optimistically with Shelley echoing the popular
saying "if Winter comes can Spring be far
behind?"