For the orthodox Israelite, Yahweh was both sovereign and vice regent occupying both 'slots' as it were at the head of the divine council. The binitarian portrayal of Yahweh in the Hebrew Bible was motivated by this belief. The ancient Israelite knew two Yahwehs one invisible, a spirit, the other visible, often in human form. The two Yahwehs at times appear together in the text, at times being distinguished, at other times not.
Early Judaism understood this portrayal and its rationale. There was no sense of a violation of monotheism since either figure was indeed Yahweh. There was no second distinct god running the affairs of the cosmos. During the Second Temple period, Jewish theologians and writers speculated on an identity for the second Yahweh. Guesses ranged from divinized humans from the stories of the Hebrew Bible to exalted angels. These speculations were not considered unorthodox. That acceptance changed when certain Jews, the early Christians, connected Jesus with this orthodox Jewish idea. This explains why these Jews, the first converts to following Jesus the Christ, could simultaneously worship the God of Israel and Jesus, and yet refuse to acknowledge any other god. Jesus was the incarnate second Yahweh. In response, as Segal's work demonstrated, Judaism pronounced the two powers teaching a heresy sometime in the second century A.D.
Here's his video on 'The Two Powers' in the Hebrew Bible
There's quite a bit on my own blog about this:
But Professor Heiser says it a lot better and with a lot more learning behind him.
His website on The Divine Council is also fascinating.