The "fear of God" is how they got people to behave back in the old days. With no way to police all of the citizens in a specific area, I think they realized they had to do something because MAN is not inherently a "nice guy."
Eh --- I dunno, that's a cynical way to look at it. I think my view that it's a mass-manipulation tool to channel sociopolitical power into the hands of the power-greedy is actually less cynical in that it means "man" (humanity) is basically good, except for those who set out to institutionalize their own greed.
Every society that's ever developed anywhere comes up with social and moral codes that keep their masses in line. They usually rely on the peer pressure of each other (real people) rather than a contrived mythical Guy-in-the-Sky. It's what we call, especially when we overdo it, "PC".