These are the possibilities that spring to mind:
- Christianity exists as is. Ex: C.S. Lewis' Space Trilogy, Darklands, Castlevania
- Overt Christianity analogue, including a Savior.
- Overt Christianity analogue absent a Savior. Ex: every JRPG, except they usually make God fake and/or evil
- Overt pre-Christianity analogue.
- Seeming paganism layered over theism. Ex: Tolkien
Problems begin to arise when we come to gameplay. Consider the typical D&D-style cleric. He can freely cast "divine spells" up to a number of times determined by his attributes and level. This is quite different from a real world wonderworker, whose every miracle-working is directly dependent upon the will of God and not on a limited reserve of power. A cleric can run out of spells; a wonderworker is done when God says he is.
Consider again, in what battle did God ever work a great miracle only to allow the beneficiary to ultimately lose? I can't think of an example. Maybe I'm just ignorant. It seems strange to imagine a character being sufficiently pious to call on God for aid in battle only for said aid, being granted, to be insufficient for victory. Such would make God look weak and ineffective.
Perhaps we try to work around these issues by not gamifying miracles at all. This has its own drawbacks. We lose the cleric, a classic archetype. The theistic religion of the setting is made to look hollow and formal rather than living and powerful. If we choose to use miracles as plot devices without allowing players access to them in gameplay, they may appear cheap contrivances. This seems to pose just as many problems as the alternative.
Then there is the matter of the details. The closer a fictional theism to Christianity, the greater also the danger of accidental blasphemy. Say you have a Christianity analogue and a cleric quotes from the equivalent of Scripture. Now you, as the writer, are inventing a pseudo-Scripture, effectively putting words in God's mouth. Fiction though it may be, if it's meant to be a stand-in for Christianity, that seems like dangerous ground to tread. Even more unsettling is the question of how to write a fictional Messiah. Perhaps this is why most don't.
One solution I've conceived is a heavily obscured approach wherein clerics receive their powers from the greater among the angels and no man is in direct communion with God. This is effectively a blend of Tolkien and D&D. Since the granters of power in this approach are finite beings and not God, it follows that the powers granted are also limited. This works well enough to avoid most conundrums, but it also is restrictive in its own way: there's no portraying the Church in all its splendor and universality.
What RPGs and other fiction handle Christianity or an analogue thereof well? and how do they so? Do you have any other thoughts on how theism ought work in RPGs?