I started reading The Book of the Long Sun, by Gene Wolfe. I read The Book of the New Sun last year and liked it a lot, so I'm trying more by the same author.
Like The New Sun, The Long Sun takes place in the distant future where technology has gone all the way, and regressed back again to a sort of fantasy setting. It centers on Patera Silk, the priest of a church in a poor quarter. They have a religion where they read randomly selected passages from their sacred text, and make live animal sacrifices in front of a big sacred computer screen in hopes that the gods will appear on it. Silk is on a quest given to him by the Outsider, the one god who does not live in the internet.
Geez, it all sounds kind of silly when I describe it! And that's before even mentioning the cyborg nun.
This has got to be the most Catholic work of fiction I have ever read. I find it bothersome, actually, though I have to admit it is interesting.
A lot of the themes in the book are about wrestling with the weaknesses of Catholicism (as Catholics see them). There's the extremely hierarchical, and sometimes-uncaring Church organization. The seemingly pointless and archaic rituals. The vow of celibacy in the holy orders. The faith and doubt in the face of divine absence. The many different conceptions of God (represented by the many gods of a polytheistic religion). And one of the major themes is loving and working closely with sinners, rather than avoiding them for fear of catching something from them (Patera Silk's friends are thieves, whores, and the like).
These are all common themes in modern Catholic self-criticism. Which is cool. But sometimes Catholics have internal conflicts which just don't translate over to a secular worldview. Like celibacy for instance: What is the point of the vow of celibacy, if any? But for me, I don't feel conflicted at all in saying that a major Catholic practice is simply pointless.
One of the interesting things about encountering religion in novels is that we as readers are free to speculate on how truthful the religion is (and which parts). Our speculations can be independent of our views of the real world. Our speculations can be right or wrong (if they are confirmed or contradicted later in the book), or they could be indeterminate (if the book leaves it open to interpretation).