In the time of ancient Sumer, there were many cities, and each city had their gods. Each god presided over different matters and each required their sacrifices and rituals. They were completely separate beings. The Egyptians – who lived in the West – said when worshiping “I have not mistaken you for any other God!” so that there would be no question of to whom they spoke.
But Sumer was not alone in the world. In time they were conquered by the Amorites and the Babylonians and the Assyrians and the Persians, all of whom had their own Gods. Of course because the Amorites and the Babylonians and the Assyrians and the Persians had won the battle, then their Gods must be stronger, so the question of whom to worship arose. Was Ashur better than Marduk? Ishtar better than Inana? And what of Ahura Mazda – who was claimed as the supreme divine authority by the Persians – and who had ever heard of such a thing?
The Persian Empire was vast, and they did not care who worshiped whom. On one end lay Greece, and on the other India, and these people mixed like peas and corn in a blender. Great king Darius hired craftsmen from the East and from the West to build his new capital Persepolis. The Greeks and Indians talked to Sumerians and Egyptians, Persians talked to Akkadians, and Israelites to Scythians, and gradually they came up with a brand new idea: perhaps there some sort of unifying principle that joined all the Gods together. They immediately started to argue about what the nature of that unifying principle might be, and their arguments spread across the empire. Both the Greeks and the Indians had much to contribute to the discussion, but India had traditions that went as deep as those in Sumeria, and maybe a little deeper, and so they had more influence. Hundreds of years later, during the reign of the great Alexander, that influence went the other way, but that is another story.
So the now-not-quite-so-ancient peoples of what had once been Sumer decided that the gods were not so separate as they had first thought, and that meant that there were different ways of interacting with the gods than they first thought. And it meant that there were different ways of living their lives than they had first thought. But, it should be said that just because these not-quite-so-ancient peoples determined that there was ONE unifying principle that they did not stop talking to the MANY gods that they knew and loved. Well, some did, but that too is another story.
So we no-longer-ancient-at-all peoples are left with this legacy. When you speak to the gods, do you speak to the One or the Many?