CS Lewis? Flakazoid. He's on, he's off, he's on again. Personally I see his vacillation about theism a market response mechanism. Tolkien had some influence on him but, ultimately, he was a writer for profit. You either embrace his writing or you do not and much can be said for the weight of his personal consideration of theism's market value. In other words, there was a fraudulent persona in his BVD's.

Tolkien - Little evidence of his perspective in LOTR trilogy, though he did conjure up some Genesis parallels in Silmarillion where Eru was the god-construct with the smattering of other good/evil parallels.

Tolkien beat Lewis up a bit over his glaring use of obvious parallels in the first Narnia nonsense. Tolkien thought he was basically usurping the bible. Lewis, on the other hand, was brought back to christianity by Tolkien's insistance and influence so though they were friends and Tolkien took him on as a fellow christian, they argued.

The summary?

It's pretty obvious that doubt is the chief characterization of christianity. People tend to hold it as near to their sensibilities as they do their faith itself. It tells us faith cannot exist in the absence of doubt, and hence the meme complex of religion to keep the faith in a defensive posture against the ever present doubt. This tells us what we've always known by their demonstrative stances, theists do not wholly buy into the god-thing. They need the constant reinforcement of religion to fend off their demons of doubt. CS Lewis was sold on his doubts. Tolkien convinced him to distance himself from them and embrace the god-construct again. A whole other book about that reality would be a good read.