Humans created "Gods" to explain natural phenomena around them, lightning, storms, earthquakes, volcanoes, any disasters that occured. It was the best way to bring order out of a chaotic (or seemingly chaotic) world. After awhile you would do things to appease the "Gods" or court them for favors......good weather, protection, etc. Next thing you know, you have priests, kings, queens, priestesses, etc, who recognize a good thing when they see it and want a piece of the action. So they start being the "divine interpreters", oracles, representative of the gods on earth, blah blah blah. They get power, control information, and hate competition....sort of like what you see today with ANY religious extremists.