So I am gonna guess the plot by using my ultra large knowledge gained by reading LN and WN and watching anime for 7 years. So from what we saw the Church is evil. They can transform into dragons but also have human form. Their god is a dragon who seems to be in "slumber''. Clearly the dragon is either the mastermind or is actually sealed and gets his blood, magic and whatever else he has stolen so the Church can get his powers. The priests eat people so they can avoid the side-effects(can be losing their life, mind and become just some beasts or simply the only way they sate their hunger). We can also see that only the ones with dragon blood in them have white hair. It seems there is some kind of instinct deep within their blood which changes the way they treat the same kind. This bishop is an arrogant being so he is surprised he accepted the request of the mc, his ''food''. The mc has white hair(limited to dragon race), his family isn't blood related and was found under a tree. So the mc can be most likely the creation, succesor or son of the dragon who has the mission of saving it and freeing the people from the Evil Church.