I think it is important to note that ceremonial burial was practiced by archaic secular societies as well - including Neanderthals. I think that we need some sort of group activity to help us transition to new situations - ie graduations, weddings, funerals, in Japan there are now wedding-like ceremonies for divorce with both families attending.

I think at its basic level there is something along these lines: change is uncertain, the group is here to witness the change and the group is not startled, I'm ok because the group is ok.