Dungeons and Dragons has traditionally been bad at depicting religion. This should come as no surprise to those who have been following the series, but it's necessary to restate it, in order to put Defenders of the Faith (Rich Redmond and James Wyatt) into context. There was no way it was ever going to be "good," because in order to be a good roleplaying book about adventurers who wield the powers of the gods, it would have to ask difficult questions about spirituality and tradition and community and metaphysics. It would have to depict people who surrendered themselves to powers beyond death and who act as a vessel for a mystery beyond words. And it could never do that, because D&D Clerics are mostly just Heal Technicians. Their religion is basically just medieval Catholicism, stripped of all purpose, complexity, and substance, distorted by a pop-culture mirror that ensures it can never rise even to the realm of the controversial. An order of sacred knights guards their Holy Grail - a chalice which caught the blood of a solar avingion as it dueled a tanar'ri. Because the paradox of the crucifixion, the holy inversion, where love defeats power, is too subtle a concept. Better to just be literal.
And I'm being something like 80% non-sarcastic here. You could maybe have a roleplaying game that dug deep into Christian theology and made it a key aspect of gameplay, but it wouldn't be Dungeons and Dragons. It probably wouldn't even be fun. And maybe that's just my bias as an atheist showing, but I'm pretty sure that the hypothetical audience for Aquinas: The Epistolary RPG of Scholastic Monasticism would not consider "fun" to be an appropriate goal. There's a spectrum here, is what I'm saying. D&D as a whole gets its place on the spectrum wrong, probably since at least the early 80s, when the Cleric class went from "thinly-veiled Van Helsing knockoff" to "key part of the campaign world's religious expression," but the worst thing you can say about Defenders of the Faith is that it doesn't move the needle significantly in either direction.
The book works well when it's ticking along inside its wheelhouse. It describes the way a "church" works - with its Services and Rituals, Expenses and Income, Charity and Advertising, and Adventurer Support and Adventuring Priests (because, oh yeah, this is an adventure game) - and if you're dealing with the deities that quite clearly take after European Jesus, it works. Pelor, Hieroneous, Saint Cuthbert - okay, this makes sense. You could probably even make Hextor work as Confederate Jesus (though, it's hurt by the fact that people in D&D world self-identify as evil, and Wizards of the Coast was not prepared to take the artistic and political risk of making a Lawful Evil religion that identified as good and valued an outward appearance of chivalry . . . you know, like the Confederacy).
However, what the fuck is supposed to be going on with the "Church of Nerull?" It's kind of a universal worldbuilding question to ask, "what are the parishioners getting out of this church," but for a neutral evil religion that explicitly only cares about cruelty and personal advancement, the question is doubly important. Are the followers propriating the God of the Undead? Are they bargaining with him to be undead themselves? Isn't that what the priests are doing? Is there a lay congregation that is hoping to one day get divine powers for themselves? How often are they successful? What's the bait on this particular hook?
These aren't impossible questions to answer. Most specific D&D settings even try to take a stab at it (with varying degrees of success), but it's incredibly out of place in this book. It couldn't even really handle the Chaotic Good and Chaotic Neutral religions. A God of Thieves is a fine concept, but what does religion even mean to a thief? Whatever it is, it probably has more to do with the tenuousness of their lives and their precarious liberty in the face of a law that wants to destroy them, and less about going to consult a priest and tithe their income to a church (even if the shrines are usually secret). You could probably take inspiration from the Mafia's weird relationship to Catholicism and talk about a thieves' guild that devoutly attended the church of Hieroneous, but that's what I mean when I say D&D is bad at religion - there is absolutely nothing in its narrative or mechanical framework that could handle that all-too-human paradox.
The Cleric class winds up having the same basic problem as the Wizard class - it's too broad a concept. It's not quite as bad, because "magic user who gains their powers from pacts with otherworldly beings" is technically a narrower niche than "magic user," but not by much. From a historical perspective, it's actually really odd to even make that split at all. So if you arrange Clerics on a line from "theurgists who serve the community in a capacity resembling medieval clergy" to "diabolists and necromancers, aesthetically indistinguishable from a dark wizard" Defenders of the Faith does well with the first type, but for the second, Tome and Blood would probably be the better resource.
Overall, this was a fine book. I enjoyed reading it. But ideally, I'm building my fantasy world in a way that renders it largely obsolete.
Ukss Contribution: I'm going to do something I don't ordinarily like to do and pick something the book explicitly says not to do. "A Paladin with scores of scrolls stuck through her belt and bandoliers of dozens of potions just looks silly."
Speak for yourself, Defenders of the Faith. Speak for yourself.