I'm looking for books like: Unsong, Canticle for Leibowitz, the Sparrow, Book of the New Sun, etc. that are all firmly science fiction while heavily featuring elements from real-world religions. If you have a recommendation that doesn't fit the question exactly but you think I'd vibe with (historical science fiction, for example), I'll award mana.
N.B.:
it must be a book I haven't read before. I don't have an exhaustive list of everything I've ever read unfortunately, but I'll award mana for a rec I've already read
I'll award mana for recommended books that fit the description even if I don't end up reading/enjoying them
1,000
1.00Hyperion by Dan Simmons is one of my top 5 sci-fi books. Part One, The Priest's Tale: "The Man who Cried God", reminds me of the Sparrow in it's portrayal of a Jesuit priest among an alien people. The Church of the Shrike and the cult based around the Shrike is also fascinating, though not based on a real-world religion.
I'll second Terra Ignota(Too Like the Lightning) and add in the Wheel of Time series, both excellent series.
Also Dune, but you might have already read that.
I liked this book. But it is a "meta" book:
Christian Horror: On the Compatibility of a Biblical Worldview and the Horror Genre
Stranger in a strange land. Might not seem religious at first glance but it's basically about a person starting a new religion.
I haven't read it but Lord of Light seems fun. Dharmic religion-inspired.
Cat's Cradle features religion heavily and is generally considered to be sci-fi. I read it but I personally didn't enjoy too much because it was too weird, but if you vibe with the specific religion in the book you might enjoy it.
Oh, and this might be an obvious one but A Handmaid's Tale. I really like this book.
If you're looking for Christian inspired books, there's also Narnia and His Dark Elements, but I suspect you heard about these already.