In those republics of gods there was always some predominating god, some real monarch. It was through the agency of this divine monarchy that primitive peoples were led from monocultism to monotheism. Hence monarchy and monotheism are twin brethren. Zeus, Jupiter, was in process of being converted into an only god, just as Jahwé originally one god among many others, came to be converted into an only god, first the god of the people of Israel, then the god of humanity, and finally the god of the whole universe.
Like monarchy, monotheism had a martial origin. "It is only on the march and in time of war," says Robertson Smith in _The Prophets of Israel_,[38] "that a nomad people feels any urgent need of a central authority, and so it came about that in the first beginnings of national organization, centring in the sanctuary of the ark, Israel was thought of mainly as the host of Jehovah. The very name of Israel is martial, and means 'God (_El_) fighteth,' and Jehovah in the Old Testament is Iahwè Çebäôth--the Jehovah of the armies of Israel. It was on the battlefield that Jehovah's presence was most clearly realized; but in primitive nations the leader in time of war is also the natural judge in time of peace."
God, the only God, issued, therefore, from man's sense of divinity as a warlike, monarchical and social God. He revealed himself to the people as a whole, not to the individual. He was the God of a people and he jealously exacted that worship should be rendered to him alone. The transition from this monocultism to monotheism was effected largely by the individual action, more philosophical perhaps than theological, of the prophets. It was, in fact, the individual activity of the prophets that individualized the divinity. And above all by making the divinity ethical.
Subsequently reason--that is, philosophy--took possession of this God who had arisen in the human consciousness as a consequence of the sense of divinity in man, and tended to define him and convert him into an idea. For to define a thing is to idealize it, a process which necessitates the abstraction from it of its incommensurable or irrational element, its vital essence. Thus the God of feeling, the divinity felt as a unique person and consciousness external to us, although at the same time enveloping and sustaining us, was converted into the idea of God.