Now 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.
He was referring to mostly Greek mythology and how it had worked itself on people. He claims the story of Christ also works like a myth but with the awareness that it actually happened.
Sheldon van Auken was a friend of Lewis. He wrote A Severe Mercy. Also a great book.
God In The Docks is another good read about the debates that CS Lewis took part in. Also, the writer fails to mention that JRR Tolkein became a Christian and was saved later in life... mostly due to this “myth” and the affect that CS Lewis had on him.