C. S. Lewis is one storied ex-atheist who ended up not only believing, but actually laboring to come up with a unifying popular theology for all Christendom, and hence his book “Mere Christianity.”
Having gone through a number of wringers myself, I think I could well refine Lewis’s approach, or at least refit it to the current of thought in the present age. But that doesn’t make Lewis’s work itself un-useful, when taken with the salt that it needs. This also hailed back to a time when Lewis’s Anglican church was more serious about the presence of Christ than it is today, over 50 years later.
I never read much of Lewis - tried to go through the Screwtape Letters and it was as torturous as The Book of Numbers in the Bible to me. Seemed he did some self-indulged working things out in his mind and published the journey rather than the wrapped up gist - of course, when my mind gets bored, I can miss a lot of the important stuff.