Two of the new girls are tied to heresy, at the very least. Not sure about morality yet. Once your heresy reaches a certain point (still testing), you get a dialogue option to summon one of two girls, a plant-type or a nightmare-type.
Still poking around to see if I can figure out what the other three unlock conditions are.
Also, the Temple reduces Heresy (~5%) and adds Rep (1, 2, etc.) for each tier you purchase. It also reduces deaths if the plague event triggers. Not sure if there are any other hidden mechanics.
I actually really like the game, but I do think it's way too easy.