I am dissatisfied with religion in D&D. Clerics are boring and don't exist in an adventuring capacity in sword and sorcery or western myth or medieval literature (with the exception of that one guy on the Bayeaux tapestry and maybe Joan of Arc) or most of the other relevant sources for D&D's tropes except the Old Testament and post-D&D works which were influenced by the game in the first place.
So, says I, let's burn 'em down and start over. Let us consider a more Greco-Nethack model of religion (yes, you read that right).
- Wisdom is changed to Piety, and explicitly models the character's ability to propitiate powerful spirits, much as Charisma models his ability to relate to other mortal beings. Wisdom / Piety continues to modify saves vs spells and RL&L rolls, as a measure of passive protection provided by the character's spirituality. Piety also modifies saves to avoid or mitigate divine retribution.
- Piety modifies prayer rolls. Anyone can pray for deliverance, but some characters are better at it than others. A successful prayer roll may duplicate a divine spell or provide another boon to the praying PC as appropriate for the deity and the circumstances; a reasonably high roll may provide the requested aid, but at future cost (failure to pay is at the supplicant's peril). A bad roll may anger the deity and bring about a curse or smiting, or it might just have no effect.
- Prayers typically fall into about-four categories:
- Deliverance from immediate peril ("Thor save us from these ghouls! Please!"). Typically manifests as minor miracles if successful. Turning undead is a lower-difficulty special case.
- Protection from an anticipated danger ("Thor, please accept these burnt goats in exchange for not capsizing our galley in a thunderstorm during our next expedition."). May manifest as blanket de-facto plot protection, or re-rolls on saves, or a bonus on saves, or a re-roll on encounter tables, or...
- Good fortune in a planned endeavour ("Thor, grant us strength in battle and bolster our courage during our raid against the orcs two islands over."). Probably primarily a limited re-roll mechanic within deity's sphere of influence.
- Guidance (Thor is probably not the best deity to pray to for guidance, but "Loki, grant us gold-wisdom in our pillaging" might work). Answers questions or bestows prophecies or what-not.
- Other circumstantial modifiers for prayer rolls are dependant on the deity in question - a jealous deity may grant a penalty if you have prayed to another deity recently, a sacrifice before the prayer may grant a bonus, and requesting aid too frequently is likely to result in some deific ire (once per week per character without penalty sounds sort of reasonable). A corrupting deity may grant a bonus in exchange for abandoning the worship of another deity. Some deities favor certain races, while others look kindly on those who follow certain codes of conduct. Which brings us to...
- Vows and taboos are codes of conduct, accepted voluntarily as part of a religious ritual. While a vow is observed, the supplicant gains a small bonus to prayer rolls for certain deities and may gain a small proficiency-like bonus or other minor boon (like a single, set low-level divine spell per day). Additionally, the vower may gain some measure of social standing within the church (bonus to reaction rolls of other worshippers). If a vow is broken, a forgiving deity may give a character an opportunity to do penance, while an unforgiving deity may make with the smiting. In either case, a vow-breaker is likely to suffer considerable social stigma within the community of worshippers of his deity.
- Oaths are similar to vows, except that while vows are mainly negative ("Thou shall not...") or routine ("Keep the sabbath holy..."), an oath is more of the form "I swear with Crom as my witness that this fortress shall not fall while I yet draw breath.". An oath compels the swearer to heroic or exceptional action. Successful completion of an oath may result in a boon (like a 10% bonus to XP earned over the course of its completion), while failure is liable to lead to smiting, cursing, or shaming by the church community. Swearing an oath which the deity finds unagreeable or rules-lawyerly is likewise cause for negative consequences. A character who dies with an oath unfulfilled may attempt prayer to be permitted to return to life or haunting undeath - otherwise, he is tormented in the afterlife for his failure.
- Quests and crusades are subsets of oaths, typically caused either by a mediocre prayer roll and required as payment by the deity, or requested by divine revelation. A quest typically requires the retrieval of a holy object and its return to the church, while a crusade usually requires the conquest of a holy land or city. Embarking on a quest may grant probationary membership of a holy military order, if any exist for the deity in question, while completion thereof is likely to result in full membership or promotion. Leading and winning a crusade may result in the crusader being proclaimed a Defender of the Faith, Hammer of Deityname, or otherwise exalted far and wide, and is also likely to result in an expansion of the victor's domains. In either case, substantial improvements in church standing result, and vows can sometimes be bent while on a quest or crusade without risking divine retribution.