Death gets put on that long list of unexplained phenomena. We don't know what death really is, except that your body stops working then starts to decompose. It was even considered unnatural at one time, and very rare for a person to die of natural causes, meaning it was unusual for someone to have lived long enough to die a natural death.
Death has to be one of the most perplexing combinations of chance and mystery since time began, wouldn't you agree? Step out into any street and you'll shortly know what I mean. The odds aren't in your favour.
It was the shock of death, usually involving violence that struck fear in mortal man. No wonder it became the catalyst that propelled religion into existence.
Death was equally disturbing when someone died of natural causes, a heart attack say, the cause old age. It took ages upon ages before man put a link to death by violence and a natural death. They knew nothing about expecting a natural end to life. It just didn't happen.
Death, at first was believed to be caused by spiritual influences. Even today, some cultures still believe certain diseases are caused by "The Enemy" (devil) and depend only on prayer to heal them. Years upon years of more complex systems of theologies ascribe death as; action from the spirit world, all of which have led to the collective belief in, "the original sin" and "the fall of man," and so on and so on. You know where I'm going with this. In other words, we're all going to die someday to pay the piper for whatever mistake Adam and Eve made in the Garden of Eden.
Imagine, the whole religion thing, it all arose from people's fear of death and the dying.