Book that combines religious themes (doubt, guilt, etc) with OCD

Something that leans thriller/horror preferred (but it doesn’t have to be)

Note: I’m not looking for a religious book. I’m agnostic. I just think. The way I felt about God as a child feels a lot like the way I felt about my OCD.

I’d love a book that explores that in a character. I refuse to believe that hasn’t been done already.