What is “Poetic Imagination” in the Philosophy of J.R.R. Tolkien, C.S. Lewis, and Owen Barfield?

Words effect what they name.

In our day and age, when so much of true art is being eviscerated and trivialized, the words of George MacDonald become increasingly poignant:

“A genuine work of art must mean many things; the truer its art, the more things it will mean.”

And:

“One difference between God’s work and man’s is that, while God’s work cannot mean more than he meant, man’s must …