As the speaker of "Ode to the West Wind" feels himself waning and decaying, he begs the wind to use him as an instrument, inhabit him, distribute his ideas, or prophesy through his mouth. He hopes to transform himself by uniting his own spirit with the larger "Spirit" of the West Wind and of Nature itself.
Because the speaker in "Ode to the West Wind" is experiencing one kind of transformation, his own gradual decline, he desires another kind of transformation, a fusion with the powers of nature.