I have a world occupied by different empires and societies with different points of view when it comes to Gods, religion etc.
Most of them are only described very briefly with just the basics since my game party has not encountered any significant worshippers of that religion, nor visited the places where such religion is popular. However, at the moment I am working on a specific religion in a desert-like area with many city states which share the same belief in Gods and I would like to hear your tips how to set their point of view towards other Gods and their worshippers.
Basically, my religion is based on a dual deity with a God of Light and a God of Night (like R'hlor in Game of Thrones with the exception that the God of Night is not evil and it is basically just another side of the same God). Their worshippers believes that this is the only God and that all the magic in the world is the gift from this God (and that is why the only sorcerers in this culture are priest dedicated to serving this God).
This, however creates an interesting dilemma. How do they look on other religions and especially other magicians from different cultures (some magicians might come to visit their cities as a part of a trading party or as adventures/scholars)? I don't want such people to be "burned on sight" (it is not supposed to be too radical religion) but I don't know how to setup the basic perception of such people...
Example: I am a priest (or just a common worshipper) who has been told that the magic comes from my God and it is the only true God. Now comes some other sorcerer from God-knows-where and he can use magic but does not worship (or even does not believe in) my God. How do I cope with that?
Of course there might have been wars caused by such conflicting religions but they are over now all the cultures (or most of them) learned that they could cooperate on some level and get over such conflicts.
How would you proceed to make the religion realistic?