Put plainly, religious exclusivity is the belief that my religion is the only true religion and the others are bullshits. (Bullshit is a PC word compared to what preachers say about people who do not belong to their religions and the traditional nomenclatures they use ranges from infidels, condemned, pagan, unsaved, children of Satan, demons, witches, etc. :Bullshit" is way, way kinder than these terms and to think that some religions even behead people who do not subscribe to their beliefs. Definitely, bullshit is much better) .
Another dogma of religious exclusivity is the conviction that only those who belong to my religion would go to paradise. Well, to tell the truth, not even all those who are in my religion would go to paradise because there's a selection process that the believers must go through like indoctrination, infant circumcision, prayers, pilgrimage, holy wars, etc. Even those who have participated and met these requisites do not automatically become saved, there is the other part, the inner conversion, the miraculous transformation of the believer, the spiritual thingy.
Now, if one sits down and give enough time and coffee to think about it, it is obvious that religious exclusivity is one of the the roots of all evil. I would not even dare say it is religion because there are religions that would not even hurt an insect!
Open your history books and you'll read that most of the man-made miseries in the world is caused by the idea of religious exclusivity. Even today, watching the current event in the Middles East I am inclined to think that this area of the world is in the dark age because the region is divided into religious factions each killing one another primarily because of the differences in the interpretation of their holy book and secondly because the schisms are being taken advantaged of by the Western primarily Christian part of the world to advance their interests.
These fanatics that came from the same religious gene cannot coexist with one another because of the effing idea that heaven is reserved to the few. Pity the innocent and the decent people who simply want to live in peace but no, they must be converted.
The idea of exclusivity goes back to the primordial soup and the microbes. Microbes based their survival in one scientific principle of physics and that is "no two objects can occupy the same space at the same time".
So, what the microbes do is multiply fast and produce enzyme or whatever you call these stuff they produce to displace another group of microbes. they congregate and those who are not within their congregation are displaced and then exterminated.
Exclusivity is a survival mechanism. It is built in to every living things' DNA from the microbes to Bill Gates. Animals form packs, herds, schools etc, to protect themselves from their predators and also these animal group protects themselves from their own kind in their struggle for food and territory. People are not that different, though we have evolved and transcended the animals' feral struggle for survival, yet exclusivity is still humanity's primary motivation for the struggle against each other though unlike the animals, people tend to cling to exclusivity more out of greed and not of need.
Socially, for us exclusivity is primarily genetics. We form group from families, to clans, to tribes, to nation from which sprung up belief system. Religion is nothing but an extension of the clan, the social family.
One current proof of exclusivity is what Trump is doing now.
It is understandable now why this idea is easily translatable into the beliefs or faiths. Religious exclusivity especially among the Abrahamic religion is primarily a survival mechanism which in the process of historical evolution has become the mechanism for oppression and control especially among its fundamentalist and fanatical adherents.