The original blog includes this quote from Alistair McGrath’s biography of C.S. Lewis which summarizes correspondence between C.S. Lewis and J.R. Tolkien:

Tolkien argued that Lewis ought to approach the New Testament with the same sense of imaginative openness and expectation that he brought to the reading of pagan myths in his professional studies. But, as Tolkien emphasized, there was a decisive difference. As Lewis expressed in his second letter to Greeves, ‘The story of Christ is simply a true myth: a myth working on us in the same way as the others, but with this tremendous difference that it really happened.‘

The reader must appreciate that the word myth is not being used here in the loose sense of a ‘fairy tale’ or the pejorative sense of a ‘deliberate lie told in order to deceive.’… For Tolkien, a myth is a story that conveys ‘fundamental things’—in other words, that tries to tell us about the deeper structure of things. The best myths, he argues, are not deliberately constructed falsehoods, but are rather tales woven by people to capture the echoes of deeper truths. They are like splintered fragments of the true light…