
The Sparrow is a novel about a remarkable man, a living saint, a life-long celibate and Jesuit priest, who undergoes an experience so harrowing and profound that it makes him question the existence of God. This experience--the first contact between human beings and intelligent extraterrestrial life--begins with a small mistake and ends in a horrible catastrophe.
The Sparrow by Mary Doria Russell is very compelling.
And I seconded it below but I'll mention it again - the Bobiverse series is excellent with amazing exploration.
https://marydoriarussell.net/novels/the-sparrow/
Almost didn't finish it. Whatever your feelings on religion are, it's a fascinating and heartbreaking exploration of how far a man can be pushed before he loses faith in his god.
(There is the book A Canticle for Leibowitz too, or at least these are the ones that I have read)
