This is from a 1944 letter to his son. Tolkien has just heard a sermon on the healing of Jairus’ daughter and is reflecting on the healing of a young boy Tolkien had witnessed in 1927.
But at the story of the little boy (which is a fully attested fact of course) with its apparent sad ending and then its sudden unhoped-for happy ending, I was deeply moved and had that peculiar emotion we all have–though not often. It is quite unlike any other sensation.
And all of a sudden I realised what it was: the very thing that I have been trying to write about and explain–in that fairy-story essay that I so much wish you had read that I think I shall send it to you. For it I coined the word ‘eucatastrophe’: the sudden happy turn in a story which pierces you with a joy that brings tears (which I argued it is the highest function of fairy-stories to produce).
And I was there led to the view that it produces its peculiar effect because it is a sudden glimpse of Truth, your whole nature chained in material cause and effect, the chain of death, feels a sudden relief as if a major limb out of joint has suddenly snapped back. It perceives–if the story has literary ‘truth’–that this is indeed how things really do work in the Great World for which our nature is made. And I concluded by saying that the Resurrection was the greatest ‘eucatastrophe’ possible in the greatest Fairy Story–and produces that essential emotion: Christian joy which produces tears because it is qualitatively so like sorrow, because it comes from those places where Joy and Sorrow are at one, reconciled, as selfishness and altruism are lost in Love.
Of course I do not mean that the Gospels tell what is only a fairy-story; but I do mean very strongly that they do tell a fairy-story: the greatest. . . . So that in the Primary Miracle (the Resurrection) and the lesser Christian miracles too though less, you have not only that sudden glimpse of truth behind the apparent ananke of our world, but a glimpse that is actually a ray of light through the very chinks of the universe about us.
–Humphrey Carpenter, ed., The Letters of J. R. R. Tolkien (New York: Houghton Mifflin, 2000), 100-101
(I reposted from this blog: http://dogmadoxa.blogspot.com/2013/01/the-greatest-fairy-story.html)