this article provides interresting origin of religious concepts
The Bible, especially the Old Testament, is full of exhortations to be cruel to heathens. Deuteronomy 20:10–18, for example, explains the obligation of the Israelites to practice genocide: when your army approaches a distant city, you should enslave all its inhabitants if it surrenders, and kill all its men and enslave its women and children and steal their cattle and everything else if it doesn’t surrender. But if it’s a city of the Canaanites or Hittites or any of those other abominable believers in false gods, then the true God commands you to kill everything that breathes in the city. The Book of Joshua describes approvingly how Joshua became a hero by carrying out those instructions, slaughtering all the inhabitants of over four hundred cities. The book of rabbinical commentaries known as the Talmud analyzes the potential ambiguities arising from conflicts between those two principles of “Thou shalt not kill [believers in thine own God]” and “Thou must kill [believers in another god].” For instance, according to some Talmudic commentators an Israelite is guilty of murder if he intentionally kills a fellow Israelite; is innocent if he intentionally kills a non-Israelite; and is also innocent if he kills an Israelite while throwing a stone into a group consisting of nine Israelites plus one heathen (because he might have been aiming at the one heathen).
In fairness, this outlook is more characteristic of the Old Testament than of the New Testament, whose moral principles have moved far in the direction of defining one’s dealings with anyone—at least in theory. In practice, of course, some of history’s most extensive genocides were committed by European colonialists against non-Europeans, relying for moral justification on the New Testament. The New Testament itself provides some explicit support for this policy: Revelations 9:4–5, for instance, says that it’s okay to torture heathens for five months, though not to kill them.
Interestingly, among New Guineans, religion is never invoked to justify killing members of an out-group. Many of my New Guinean friends have described to me their participation in genocidal attacks on neighboring tribes. In all those accounts, I have never heard the slightest hint of any religious motive, of dying for God or the true religion, or of sacrificing oneself for any idealistic reason whatsoever. The religion-supported ideologies that accompanied the rise of states instilled into their citizens the obligation to obey the ruler ordained by God, to obey moral precepts like the Ten Commandments only with respect to fellow citizens, and to be prepared to sacrifice their lives while fighting against other states (i.e., heathens). That’s what makes societies of religious fanatics so dangerous: a tiny minority of their adherents (e.g., nineteen of them) die for the cause, and the whole society of fanatics thereby succeeds at killing far more of its perceived enemies (e.g., 3,025 of them).
Wilson explains that fanatical religious sects, such as expansionist Islam and Christianity, spread as a result of group selection operating at the level of human societies: those early state societies whose religions were especially effective at motivating their citizens to sacrifice themselves succeeded in defeating societies with less motivating religions. Fictitious beliefs —such as the belief that a heaven populated by beautiful virgins awaits those who die for the cause—can contribute powerfully to effective motivation.
Rules of bad behavior toward out-groups reached their high point in the last 1,500 years, as fanatical Christians and Muslims inflicted death, slavery, or forced conversion on the heathen. Within the twentieth century, European states have turned instead to secular grounds to justify killing millions of citizens of other European states, but religious fanaticism is still strong in some other societies.