I love Pratchett's take on religion and religious philosophy. The small god, Om, currently in the shape of a turtle, has lost his power due to a lack of true believers. Om needs a disciple. Unfortunately the gentle Brutha is the only one available. This is a standalone in the Discworld series, with none of the usual cast of characters. It contains some profound ideas about religion and what humans do (or try to do) in its name. Mr P has some things to say about religion, but never loses the humour and absurdity that Discworld is known for.