I intend to branch off from the tutorial at some point and have the game be about playing as St. Anthony being tested in the desert. I think the core gameplay mechanics should be a spellcrafting system and a faith system.
Spellcrafting System A limited number of discrete spell attributes that can be combined to form spells.
Faith System Some kind of 'mana' esque system that's based on player decision making. This may be beyond my abilities, but if thematically the player is playing as a Saint, there should be come component in the gameplay that relates to that.