Rev Gal Blog Pals had a question come into their "Ask the Matriarch" column asking what children's books would be good for a pastor's bookshelf.
In thinking about the books that most strongly made me think about my concept of god and my relationship to faith, I realized that most of them are Science Fiction or Fantasy. Not only that, but they are books that made me think. I don't know that a priest would want to have these books on their bookshelf (I suspect they might offend some sensibilities) but they were instrumental in my faith journey.
The following are books that spoke to me when I was a kid-to-teen reader and newer books that I wish I had had back then.Madeline L'Engle's "Wrinkle in Time" trilogy (Wrinkle in Time, A Wind in the Door, and A Swiftly Tilting Planet).
C.S. Lewis's Narnia series (read in publication order, please!) :).
His Perlanda series is also good, but a little weird, and I found the last book too scary to read initially (the cover scared me). I remember reading several of his other works (The Screwtape Letters is the only specific title I can remember) and finding them interesting as a teen.
Frank Herbert and poet Bill Ransom had a series of science fiction books that I liked as a teenager-- not sure how they hold up now: "Destination: Void," "The Jesus Incident," "The Lazarus Effect," and "The Ascension Factor." (I have not read the fourth book-- I just found out about while looking up the titles of the first three).
As an adult I discovered the Terry Prachett Discworld series-- those are excellent for thinking about human relationships, and relationships to the divine while being entertained. "Feet of Clay" and "Small Gods" are particularly interesting from a religious standpoint. (Though "Small Gods" might be too grim for younger readers). The thing about Terry Prachett's work is that if you were one of the characters experiencing the events it wouldn't be the least bit funny, but the way he frames the setting his word choice makes his books easy to read, fun, and yet a bit spiky. He has a series that is more specifically aimed at younger readers (starting with "Wee Free Men") that features a young girl as the protagonist. I don't know that they have particularly religious themes in them, but really any fiction contains the seeds of theological reflection.
One book I was giving away to everyone I knew for a while was "Beauty" by Sherri Tepper. It is also better suited for older readers (includes scenes of violence and rape) but explores the human need for beauty and mystery and what might happen to us if we lose both our real and mythological 'wild' places.
I include the "Thomas Covenant" books in the interest in completeness. It was the first book I read with a (vile) anti-hero as the protagonist and several things about it creeped me out, however it did have an interesting concept of god and free will-- something I reflected on often while in my teens.
Another series that came out when I was an adult is Lois McMaster Bujold's fantasy series that begins with "The Curse of Chailon." My favorite in the series is second book: "The Paladin of Souls." In this universe, gods clearly exist, but can only move in the world if a person opens their soul to the divine. A lovely, gritty, exploration of what it means to ask for a miracle.
I'm sure there are more-- but these are the ones I could clearly remember having an impact on how I viewed the world. Looking back over this list, one of the things it brings to mind is the fact that my parents, while very happy to censor my TV and film viewing, never put any limits on which books I read. That freedom to choose was a wonderful gift and led me to discover many wild imaginary lands.