Religions and Religious beliefs are ubiquitous across times, and countries and cultures. From the perspective of Evolution it signals that it has Evolutionary survival value. It seems to me that human beings by virtue of simply being alive experience Existential anxiety at the awareness that our personal death and that of our family friends and loved one loom ahead and that we Exist in a boundlessly Mysterious universe....Organized Religion seems to offer an answer to that background anxiety all folks experience and answers to the Questions that surge in human minds about being alive in this Universe.
I can appreciate what you're saying here and I agree with certain aspects. Human spirituality does indicate evolutionary survival value, that's hard to deny. The question is, why? So we can surmise as you have, that it's because humans realize their own mortality and experience existential anxiety. That's an easy enough explanation until you start to ponder how the hell did we contemplate existentialism or immortality to begin with? It's kind of like the chicken or egg dilemma. Other species of life don't seem to have this problem grappling with their own mortality. So this tells me that it's possibly the other way around, we didn't invent spirituality to cope with our anxiety, the anxiety was created by our spirituality which already existed.
Religion is simply a manifestation of our inherent spirituality. We are creatures who are hard-wired with an inherent "sense" of something beyond ourselves. We don't know what it is, we can't really define it, but we are spiritually aware and connected to it. Religions serve as a placeholder for those senses and we obtain a semblance of solitude through religious connection with others.
I prefer to view The Church (organized religion) as sort of a "health club" for human spirituality. Now, lots of people believe in maintaining good physical health but they don't necessarily believe they need to join a health club. They have the inner discipline to exercise and maintain their health without the need for a place to go. Others might find it beneficial and that's fine, there's nothing wrong with that. I don't go around bashing religion because I think it's an important aspect for a lot of people. It's how they feel they can spiritually connect the best.