I recall, at some point in my past, reading about how C.S. Lewis utilized pagan imagery from the past--imagery that was once taken seriously by the pagans of those ancient times--and transforming them into a myth that can be bent and used for the greater purpose of God's glorification.  

But where has this discussion taken place?  Is it in an essay somewhere?  A book?  Where can I find this?

The case of C.S. Lewis is very tragic.  Here is a man who, like Chesterton and Belloc had lost any faith he may have had in his youth.  But when he actually started to consider the Christian religion he realized its truth.  Unlike Chesterton and Belloc, however, after investigating the One True Christian Religion, Catholicism, he rejected it and opted instead for the heretic sect, Anglicanism.

He cannot even be given the benefit of doubt of "invincible ignorance" (if such a thing truly exists) because he investigated Catholicism very carefully but declared that he could not cross that bridge his friends had crossed.  Whether it was out of a sense of patriotism to his country or some article of faith he could not accept, he rejected the True Faith.

Very tragic, indeed.