Here’s how Auden explained it in his essay “Some Reflections on the Arts”:
Every genuine work of art exhibits two qualities, Nowness—an art-historian can assign at least an approximate date to its making—and Permanence—it remains on hand in the world long after its maker and his society have ceased to exist.
This means that, in the history of Art, unlike the history of Science, though there are periods of flowering and sterility, there is no such thing as Progress, only Change. Shakespeare does not supersede Aeschylus or Mozart Moteverdi, in the way that the Copernican picture of the Cosmos, for example, superseded the Ptolemaic.
Consequently, one of the greatest blessings conferred on our lives by the Arts is that they are our chief means of breaking bread with the dead, and I think that, without communication with the dead, a fully human life is not possible.