Why do people have wars over religious beliefs?

If religious beliefs come from religious text and text is written by man then why do people feel so pionate about it to risk every thing. I will rephrase: Me and a person on the street can see each other living. We know that we exist. say this person and I are at war based on ideals from a book that tells us of things that we can not see, we can not touch but yet we fight and kill based on these things we have been told. things that have no factual proof. yet we know that the person in front of us exist. Why do we take the word of a book over the life of a person in front of us? Is it for our own hopeful salvation in a after world construed by text we so willingly adopt as life law and practice? if so I think it is selfishness