Small Gods - Terry Pratchett

Terry Pratchett's Small Gods is a good place to start reading the Discworld books - it's a stand-alone (ie. not part of a several-books-long character arc) and it's not too outrageously funny (which some people might find off putting). It's also profound, very thought-provoking and still very relevant (in some ways it's more relevant), despite being written nearly 14 years ago.

The setting is the country of Omnia, a land on the Klatchian coast of the Discworld, that is ruled by the priesthood of the Church of Om. It's a harsh, arid desert country where the Quisition works tirelessly (and bloodily) to remove the sin from individuals deemed to be guilty - and almost no one is safe from the Quisition, since the priests regard the very existence of suspicion as proof of guilt. You might think that the Great God Om would bask in the power and glory of his church, but ritual has replaced substance in Omnia, and whilst the people worship Om, they don't really believe in him anymore. As a consequence, when Om manifested himself three years ago, he found himself stuck in the body of a one-eyed tortoise (rather than, say, a mighty bull, as he was planning) and he has only just found someone with the true flame of faith burning inside him. Unfortunately for Om, that one believer is Brutha, a novitiate in the Church whom, all would agree, is just a little bit slow on the uptake, and is probably the last person Om would have chosen to become his new Prophet. Brutha does have one thing going for him - he has a perfect memory, but unfortunately, because he remembers literally everything, he has little spare brain capacity for thought. Although, in a way, this is not hugely inconvenient since the Church strongly discourages individuals who think for themselves as that kind of thing just leads to trouble.

Unsurprisingly Brutha has a hard time accepting that a tortoise is the Great God Om, and since Om doesn't have the power to do anything but mouth ineffectual curses at the things that bother him, Om cannot easily convince Brutha of his identity. Brutha becomes increasingly disturbed to learn that Om never really gave his followers any instruction whatsoever - all of the holy books that he knows by heart were apparently made up by the prophets. Then Brutha finds himself accompanying Deacon Vorbis, the head of the Quisition, to the land of Ephebe, where you can't throw a brick without hitting a philosopher, all of whom argue violently among themselves, and frequently live in barrels. One such philosopher is Didactylos, whose philosophy is summed up as "It's a funny old world". He suddenly finds himself part of an underground movement that insists, despite the tenets of the Omnian Church, that "the Turtle moves"; that turtle being Great A'Tuin, the space-faring turtle on whose back the Discworld is carried by four elephants. As so often happens, religious dispute breeds war, and the future of Omnia - not to mention the future of the Great God Om - lies in the hands of Brutha and how he deals with others, particularly Deacon Vorbis.