I don't think the main reasons are spiritual, or about fear of death.
I think it's mainly about responsibility-- we are just smart enough to know how god-damned complex the world is, and work ourselves into a pretty major panic attack if we think about it too much. Religion gives you a proxy to carry that psychological weight for you. Basically, you are meant to get out of bed, go to work, make and raise your babies, and never forget to donate to the church-- you are not to sit around thinking too much about shit you can't control, anyway.
I think it's mainly about responsibility-- we are just smart enough to know how god-damned complex the world is, and work ourselves into a pretty major panic attack if we think about it too much. Religion gives you a proxy to carry that psychological weight for you. Basically, you are meant to get out of bed, go to work, make and raise your babies, and never forget to donate to the church-- you are not to sit around thinking too much about shit you can't control, anyway.
