As I understand it, correction invited if I'm wrong, it was standard in the ancient world for the highest religious offices to be occupied by those also in the highest political offices. That is there was no way to separate the religious and the secular authorities. I was struck today as I read Numbers 27 by vs20-21, Moses has prayed about his successor in leadership and God replies that Joshua will be that successor,
You shall give him some of your authority, so that all the congregation of the Israelites may obey. But he shall stand before Eleazar the priest who shall inquire for him . . . before the LordUp to this point Moses had been both the leader of the Israelites and the one responsible for mediating God's voice to the people. Here Joshua is set up as leader but only some of Moses authority is passed on to him, and the rest presumably passes to Eleazar, a separation of church and state, of religious and secular power. This also presumably sets the scene for the prophetic interaction with the kingly office that occupies much of the subsequent OT - the idea that the leader of the people is not supreme but can guided and if necessary called to account by a separate religious institution.