"The echo of the tune we have not heard"

John Piper begins his explanation of the importance of C.S. Lewis by describing various ways he thinks Lewis's theology inadequate. Some evangelicals consider such problems sufficient reason to dismiss Lewis entirely. Piper doesn't, and explains why in "Lessons from an Inconsolable Soul," [listen here]:

.... The answer lies in the way that the experience of Joy and the defense of Truth come together in Lewis’s life and writings. The way Lewis deals with these two things—Joy and Truth—is so radically different from Liberal theology and emergent postmodern slipperiness that he is simply in another world—a world where I am totally at home, and where I find both my heart and my mind awakened and made more alive and perceptive and responsive and earnest and hopeful and amazed and passionate for the glory of God every time I turn to C. S. Lewis. It’s this combination of experiencing the stab of God-shaped joy and defending objective, absolute Truth, because of the absolute Reality of God, that sets Lewis apart as unparalleled in the modern world. To my knowledge, there is simply no one else who puts these two things together the way Lewis does. [....]

Piper explains exactly how important Lewis's presentation of these two themes have been to his understanding. With respect to "Joy," part of what Piper writes (I've omitted Piper's footnotes):

The experience of this Joy is the most important theme of his life. He says so. It gives unity to everything else. He said of this experience, “In a sense the central story of my life is about nothing else.” Very seldom does a writer tell us what he believes is the central theme of his life. Lewis does tell us. Everything in his life gains its deepest meaning from its connection with this.

Here’s the closest thing that Lewis gives to a definition of this Joy: It is the experience “of an unsatisfied desire which is itself more desirable than any other satisfaction.” This is why he chose the word Joy rather than “desire” or “longing” or “Sehnsucht” when writing his autobiography—because those words failed to convey the desirability of the longing itself.

I call it Joy, which is here a technical term and must be sharply distinguished both from Happiness and from Pleasure. Joy (in my sense) has indeed one characteristic, and one only, in common with them; the fact that any one who has experienced it will want it again. Apart from that, and considered only in its quality, it might almost equally well be called a particular kind of unhappiness or grief. But then it is the kind we want. I doubt whether anyone who has tasted it would ever, if both were in his power, exchange it for all the pleasures in the world. But then Joy is never in our power and pleasure often is.

Or again he says, “Joy is distinct not only from pleasure in general but even from aesthetic pleasure. It must have the stab, the pang, the inconsolable longing.” So on the one hand, Joy has this dimension of “inconsolable longing,” aching, yearning for something you don’t have. But on the other hand, the longing and aching and yearning is itself pleasurable. It is in itself not just a wanting to have but a having.

True, it was desire, not possession. But then what I had felt on the walk had also been desire, and only possession in so far as that kind of desire is itself desirable, is the fullest possession we can know on earth; or rather, because the very nature of Joy makes nonsense of our common distinction between having and wanting. There, to have is to want to want is to have. Thus, the very moment when I longed to be stabbed again, was itself again such a stabbing.

Alan Jacobs is right to say, “Nothing was closer to the core of his being than this experience.” And perhaps what sealed its significance for Lewis is that it brought him to Christ. He was an atheist in his twenties, but relentlessly God was pursuing him through the experience of “inconsolable longing.” And he was finding that the writers who awakened it most often were Christian writers. (....)

Lewis looked back on all his experiences of Joy differently now. Now he knew why the desire was inconsolable, and yet pleasant. It was a desire for God. It was evidence that he was made for God.

The books or the music in which we thought the beauty was located will betray us if we trust to them; it was not in them, it only came through them, and what came through them was longing. These things—the beauty, the memory of our own past—are good images of what we really desire; but if they are mistaken for the thing itself, they turn into dumb idols, breaking the hearts of their worshipers. For they are not the thing itself; they are only the scent of a flower we have not found, the echo of the tune we have not heard, news from a country we have never yet visited.

All his life, he said, “an unattainable ecstasy has hovered just beyond the grasp of [my] consciousness.” “The sweetest thing of all my life has been the longing . . . to find the place where all the beauty came from.” But when Lewis was born again to see the glory of God in Christ, he never said again that he didn’t know where the beauty came from. Now he knew where all the joy was pointing. On the last page of his autobiography, he explained the difference in his experience of Joy now and before.

I believe...that the old stab, the old bittersweet, has come to me as often and as sharply since my conversion as at any time of my life whatever. But I now know that the experience, considered as a state of my own mind, had never had the kind of importance I once gave it. It was valuable only as a pointer to something other and outer. While that other was in doubt, the pointer naturally loomed large in my thoughts. When we are lost in the woods the site of the signpost is a great matter. He who first sees it cries, ‘Look!’ The whole party gathers around and stares. But when we have found the road and are passing signposts every few miles, we shall not stop and stare. They will encourage us and we shall be grateful to the authority that set them up. But we shall not stop and stare, or not much; not on this road, though their pillars are of silver and their lettering of gold. ‘We would be at Jerusalem.’

So Lewis stopped turning Joy into an idol when he found, by grace, that it was “a pointer to something other and outer,” namely to God. Clyde Kilby gave the highest estimation of this theme in Lewis:

[For Lewis Joy is] a desire which no natural happiness can ever satisfy, the lifelong pointer toward heaven . . . which gave us such delight and yet are the meager signs of the true rapture He has in heaven for redeemed souls. . . . The culmination of Sehnsucht [Longing, Joy] in the rhapsodic joy of heaven is, for me at least the strongest single element in Lewis. In one way or other it hovers over nearly every one of his books and suggests to me that Lewis’s apocalyptic vision is perhaps more real than that of anyone since St. John on Patmos.

There is much more, including discussion of Lewis on objective Truth, "chronological snobbery," and so on.

Update [2/5]: Desiring God has put video of Piper's address online:

Lessons from an Inconsolable Soul :: Desiring God Christian Resource Library