Walter M. Miller Jr.'s A Canticle for Leibowitz (1960) is one of the most celebrated books in all of science fiction, a post-apocalyptic novel about the endurance of the Catholic Church and the inevitability of man's self-destructiveness as a species. I've known about the book for as long as I've been reading science fiction (since my early teens), but for some reason I never read it until now. I'm glad to say I now understand why it's achieved the renown it has. One reason is that he's a damn good writer: the prose is an order of magnitude better than any other SF coming out of the 1960s, except possibly Ursula Le Guin. Another reason is that he's created an incredibly enduring look at the apocalypse: he postulates a society slightly more advanced than ours that's destroyed itself in a nuclear holocaust, and the entire novel takes place across centuries after that event. Most science fiction "ages out," with their predictions becoming blatantly incorrect. He starts by blowing up our society, and from there on his speculation is ... universal.
The novel is in three parts, the first of which amounts to the Dark Ages. It establishes the Catholic Order of St. Leibowitz, which preserves "the Memorabilia" - documents of science and technology from before the "Flame Deluge." The second part is essentially a Renaissance, and the third amounts to the equivalent of our 21st century - a technology slightly more advanced than that of 2016.
Miller seems to have a very high opinion of the Catholic Church. Most of the major characters are priests and abbots and, while each is a fully developed character (and he's very good at character), they're all good people doing the right thing. I wonder if his characterization of the church would have been significantly different if he'd written the book after the revelations of the sexual abuse scandal in Boston (and the rest of the world). (I'm aware that this doesn't condemn the entire church ... but his view of it is more positive than I think is warranted.)
This is not an upbeat book. He believes - and argues very convincingly - that we're condemned to repeat our mistakes and destroy ourselves. But it's a superbly written story that should be read by not just fans of the genre, but by everyone.