W. H. Auden explains:

Every poet, consciously or unconsciously, holds the following absolute presuppositions, as the dogmas of his art:

(1) A historical world exists, a world of unique events and unique persons, related by analogy, not identity. The number of events and analogical relations is potentially infinite. The existence of such a world is a good, and every addition to the number of events, persons and relations is an additional good.

(2) The historical world is a fallen world, i.e. though it is good that it exists, the way in which it exists is evil, being full of unfreedom and disorder.

(3) The historical world is a redeemable world. The unfreedom and disorder of the past can be reconciled in the future.

It follows from the first presupposition that the poet’s activity in creating a poem is analogous to God’s activity in creating man after his own image. It is not an imitation, for were it so, the poet would be able to create like God ex nihilo; instead, he requires pre-existing occasions of feeling and a pre-existing language out of which to create. It is analogous in that the poet creates not necessarily according to a law of nature but voluntarily according to provocation.

(stolen from Alan Jacobs)