The belief in a single God, or a religion affirming that belief, as opposed to polytheism, belief in many deities. There does not seem to be a time when Israelite worship was officially, as portrayed in the sources, other than monotheistic, though historically it may have evolved out of henotheism such as was typical in the area. The 9th‐cent. Moabite Stone refers to the national god Chemosh without denying the existence of other divinities. The Hebrews worshipped Yahweh as their national god and there are OT allusions to other nations' gods which imply a belief in their existence, alongside Israel's Yahweh. Such gods, it was held, were worshipped legitimately in their own country (1 Sam. 26: 19). Now and then undisguised polytheism crept in by the monarch's back door, as when Yahweh was allocated a female consort (1 Kgs. 11: 5), and opposite the Temple were built shrines to Kemosh and Milcom. The prophets were zealous in opposition and in the 7th cent. BCE these shrines were demolished by Josiah. In Deuteronomy, monotheism was linked to strong ethical demands (Deut. 6: 4) and after the Exile there was no looking back: Second Isaiah (Deutero‐Isaiah) accepts that Yahweh is responsible for both good and evil (Isa. 45: 7). He can ridicule polytheism without serious comprehension of it but also without any expectation of being contradicted. Nevertheless, even when belief in the one God was fundamental, there remained traces of recognition of subordinate deities (Job 1–2) and the existence of angels and of Satan was also assumed.

Monotheism continues to be taken for granted in the NT (Mark 12: 29; 1 Cor. 8: 6), together with the existence of subordinate angels (Heb. 1: 4), and polytheism was blamed for the horrors of immorality (Rom. 1: 24–31). But trouble was imminent when Christians found themselves giving worship to Jesus. Jewish opponents accused them of abandoning monotheism. The Christian answer, after agonizing speculations and deviations, eventually issued in the doctrine of the Trinity.