The true myth

In "The Inklings Were Not Closet Pagans" Louis Markos corrects a reviewer's misapprehension:

...[T]he love for paganism that Lewis, Tolkien, Barfield, and Williams shared rose up out of their belief that the myths and sagas of the Norsemen, together with those of Greece and Rome, were filled with glimpses of greater divine truths whose fullness would not be revealed until the coming of Christ. Indeed, it was this very belief—that Christ fulfilled not only the Old Testament Law and Prophets but the good dreams of the pagans—that led Lewis from a generic belief in theism to a radical faith in Jesus Christ as the Son of God.

The person who opened his eyes to this belief was none other than Tolkien. In answer to Lewis’s argument that Christ was merely the Hebrew version of the pagan myth of the dying and rising God, Tolkien replied that the reason for the parallels between Balder, Adonis, Osiris, and Mithras on the one hand and Jesus of Nazareth on the other was that Jesus was the myth that became fact.

For the Inklings, Christianity was a religion that, though fixed in history (Jesus died and rose again in real time and space at a specific moment in human history), was also bathed with the warm glow of myth. As such, it appeals with equal power to our reason and our imagination, to our adult logic and our childlike wonder, to our search for truth and our hunger for meaning. (more)

From Tolkien's "On Fairy Stories" included in his Tree and Leaf:

The Gospels contain a fairy story, or a story of a larger kind which embraces all the essence of fairy-stories. They contain many marvels—peculiarly artistic, beautiful, and moving: “mythical” in their perfect, self-contained significance; and among the marvels is the greatest and most complete conceivable eucatastrophe. But this story has entered History and the primary world; the desire and aspiration of sub-creation has been raised to the fulfillment of Creation. The Birth of Christ is the eucatastrophe of Man's history. The Resurrection is the eucatastrophe of the story of the Incarnation. This story begins and ends in joy. It has preeminently the “inner consistency of reality.” There is no tale ever told that men would rather find was true, and none which so many sceptical men have accepted as true on its own merits. For the Art of it has the supremely convincing tone of Primary Art, that is, of Creation. To reject it leads either to sadness or to wrath.

It is not difficult to imagine the peculiar excitement and joy that one would feel, if any specially beautiful fairy-story were found to be “primarily” true, its narrative to be history, without thereby necessarily losing the mythical or allegorical significance that it had possessed. It is not difficult, for one is not called upon to try and conceive anything of a quality unknown. The joy would have exactly the same quality, if not the same degree, as the joy which the “turn” in a fairy-story gives: such joy has the very taste of primary truth. (Otherwise its name would not be joy.) It looks forward (or backward: the direction in this regard is unimportant) to the Great Eucatastrophe. The Christian joy, the Gloria, is of the same kind; but it is preeminently (infinitely, if our capacity were not finite) high and joyous. But this story is supreme; and it is true. Art has been verified. God is the Lord, of angels, and of men—and of elves. Legend and History have met and fused. (my emphases)

The Inklings Were Not Closet Pagans, J.R.R. Tolkien, One Fairy Stories