In "Ode to the West Wind," why does Shelley call the West Wind "destroyer" and "preserver"?
Shelley's "Ode to the West Wind" was written within the Romantic tradition, and utilizes common Romantic tropes such as the personification of Nature and the invocation of pathetic fallacy, wherein Nature has human attributes and motivations. As a great natural power, then, Shelley's "West Wind" is both creative and destructive, a force to which humans are subject.
At the beginning of the poem, Shelley describes the West Wind as the "breath of Autumn's being," suggesting a vibrant and living force which drives away dead things before it—"like ghosts from an enchanter fleeing." In this way, the Wind clears the path for new life to emerge, establishing it as a creative force. It is the Wind which "chariotest [conveys] to their dark wintry bed/the winged seeds." While the seeds will lie "each like a corpse within its grave" until summer, without the strong winds of winter, a space could not have been cleared for them to grow in when the time is right. For this reason, the West Wind can be seen as a "preserver," maintaining the cycle of life and death in nature and preserving the balance.
At the same time, of course, the Wind's destructive properties cannot be forgotten. As the "dirge of the dying year," its song is a symbol that the havoc of winter is about to be wreaked upon the earth, with the Wind generating an atmosphere from which "black rain, hail and fire will burst." While the coming of winter is a necessary part of a cycle of renewal, the West Wind can also have devastating effects upon those who fall prey to its "uncontrollable" whims.