From the Introduction:

I told a Christian friend I’d become an atheist. He replied that it would be interesting if I told people what that feels like. The phrase stayed with me. “What that feels like.” I wrote this book for him. It’s not about religion. It is especially not an invitation to debate God or other theological or doctrinal issues. I’m not out to convert or unconvert anybody. It’s about a guy who went from believing to thinking, then looked around and found himself in a world without God.