From C.S. Lewis through the Shadowlands by Brian Sibley pp 51-52

“What Dyson and Tolkien showed me,” he [C.S.Lewis] wrote, “was that if I met the idea of sacrifice in a Pagan story I didn’t mind it all: again, that if I met the idea of a god sacrificing himself to himself I liked it very much and was mysteriously moved by it: again, that the idea of the dying and reviving god similarly moved me provided I met it anywhere except in the Gospels.”

With Tolkien’s help , Jack [Lewis] began to see Christianity in relation to the myths he already loved, began to believe that “the story of Christ is simply a true myth: a myth working on us in the same way as others, but with the tremendous difference that it really happened: and one must be content to accept it in the same way, remembering that…