Some Saturday C. S. Lewis" was introduced and explained here. The following quote is from the essay "The Weight of Glory", now published in the essay and sermon compilation by the same name.
God has given us the Morning Star already: you can go and enjoy the gift on many fine mornings if you get up early enough. What more, you may ask, do we want? Ah, but we want so much more--something the books on aesthetics take little notice of. But the poets and the mythologies know all about it.
We do not want merely to see beauty, though, God knows, even that is bounty enough. We want something else which can hardly be put into words--to be united with the beauty we see, to pass into it, to receive it into ourselves, to bathe in it, to become part of it. That is why we have peopled air and earth and water with gods and goddesses and nymphs and elves--that, though we cannot, yet these projections can, enjoy in themselves that beauty, grace, and power of which Nature is the image.
That is why the poets tell us such lovely falsehoods. They talk as if the west wind could really sweep into a human soul; but it can't. They tell us the 'beauty born of murmuring sound' will pass into a human face; but it won't. Or not yet. For if we take the imagery of Scripture seriously, if we believe that God will one day give us the Morning Star and cause us to put on the splendour of the sun, then we may surmise that both the ancient myths and the modern poetry, so false as history, may be very nearly prophecy.
At present we are on the outside of the world, the wrong side of the door. We discern the freshness and purity of morning, but they do not make us fresh and pure. We cannot mingle with the splendours we see. But all the leaves of the New Testament are rustling with the rumour that it will not always be so. Some day, God willing, we shall get in.