It has traditionally been believed that monotheism was part of Israels original covenant with Yahweh on Mount Sinai, and the idolatry criticized by the prophets was due to Israels backsliding. But during the 20th century it became increasingly recognised that the Bibles presentation raises a number of questions: Why do the Ten Commandments declare that there should be no other gods before Me (Yahweh), if there are no other gods at all? Why do the Israelites sing at the crossing of the Red Sea that there is no god like you, O Yahweh, implying that other gods exist? These observations eventually overthrew the belief that Israel had always worshipped no other god but Yahweh.
Israelite gods other than Yahweh in fact appear frequently, both in the bible and the archaeological record. Respectful references to the goddess Asherah or her symbol, for example, as part of the worship of Yahweh, are found in the eighth century inscriptions from Kuntillet Ajrud and Khirbet el-Qom, and the gods Resheph and Deber appear without criticism in Habakkuk 3:5 as part of the military retinue of Yahweh. Similarly, the hosts of heaven are mentioned without criticism in 1_Kings 22:19 and Zephaniah 1:5, and the god El is continually identified with Yahweh.
Israel inherited polytheism from late first-millennium Canaan, and Canaanite religion in turn had its roots in the religion of second-millennium Ugarit. In the 2nd millennium, polytheism was expressed through the concepts of the divine council and the divine family, a single entity with four levels: the chief god and his wife (El and Asherah); the seventy divine children or stars of El (including Baal, Astarte, Anat, probably Resheph, as well as the sun-goddess Shapshu and the moon-god Yerak); the head helper of the divine household, Kothar wa-Hasis; and the servants of the divine household, including the messenger-gods who would later appear as the angels of the Hebrew bible.
In the earliest stage Yahweh was one of the seventy children of El, each of whom was the patron deity of one of the seventy nations. This is illustrated by the Dead Sea Scrolls and Septuagint texts of Deuteronomy 32:8-9, in which El, as the head of the divine assembly, gives member of the divine family a nation of his own, according to the number of the divine sons: Israel is the portion of Yahweh. The later Masoretic text, evidently uncomfortable with the polytheism expressed by the phrase, altered it to according to the number of the children of Israel
Between the eighth to the sixth centuries El became identified with Yahweh, Yahweh-El became the husband of the goddess Asherah, and the other gods and the divine messengers gradually became mere expressions of Yahwehs power. Yahweh is cast in the role of the Divine King ruling over all the other deities, as in Psalm 29:2, where the sons of God are called upon to worship Yahweh; and as Ezekiel 8-10 suggests, the Temple itself became Yahwehs palace, populated by those in his retinue.
It is in this period that the earliest clear monotheistic statements appear in the Bible, for example in the apparently seventh-century Deuteronomy 4:35, 39, 1 Samuel 2:2, 2 Samuel 7:22, 2 Kings 19:15, 19 (= Isaiah 37:16, 20), and Jeremiah 16:19, 20 and the sixth-century portion of Isaiah 43:10-11, 44:6, 8, 45:5-7, 14, 18, 21, and 46:9. Because many of the passages involved appear in works associated with either Deuteronomy, the Deuteronomistic History (Joshua through Kings) or in Jeremiah, most recent scholarly treatments have suggested that a Deuteronomistic movement of this period developed the idea of monotheism as a response to the religious issues of the time.
The first factor behind this development involves changes in Israels social structure. At Ugarit, social identity was strongest at the level of the family: legal documents, for example, were often made between the sons of one family and the sons of another. Ugarits religion, with its divine family headed by El and Asherah, mirrored this human reality. The same was true in ancient Israel through most of the monarchy - for example, the story of Achan in Joshua 8 suggests an extended family as the major social unit. However, the family lineages went through traumatic changes beginning in the eighth century due to major social stratification, followed by Assyrian incursions. In the seventh and sixth centuries, we begin to see expressions of individual identity (Deuteronomy 26:16; Jeremiah 31:29-30; Ezekiel 18). A culture with a diminished lineage system, deteriorating over a long period from the ninth or eighth century onward, less embedded in traditional family patrimonies, might be more predisposed both to hold the individual accountable for his behavior, and to see an individual deity accountable for the cosmos. In short, the rise of the individual as the basic social unit led to the rise of a single god replacing a divine family.
The second major factor was the rise of the neo-Assyrian and neo-Babylonian empires. As long as Israel was, from its own perspective, part of a community of similar small nations, it made sense to see the Israelite pantheon on par with the other nations, each one with its own patron god - the picture described with Deuteronomy 32:8-9. The assumption behind this worldview was that each nation was as powerful as its patron god. However, the neo-Assyrian conquest of the northern kingdom in ca. 722 challenged this, for if the neo-Assyrian empire were so powerful, so must be its god; and conversely, if Israel could be conquered (and later Judah, c. 586), it implied that Yahweh in turn was a minor divinity. The crisis was met by separating the heavenly power and earthly kingdoms. Even though Assyria and Babylon were so powerful, the new monotheistic thinking in Israel reasoned, this did not mean that the god of Israel and Judah was weak. Assyria had not succeeded because of the power of its god Marduk; it was Yahweh who was using Assyria to punish and purify the one nation which Yahweh had chosen.
By the post-Exilic period, full monotheism had emerged: Yahweh was the sole God, not just of Israel, but of the whole world. If the nations were tools of Yahweh, then the new king who would come to redeem Israel might not be a Judean as taught in older literature (e.g. Psalm 2). Now, even a foreigner such as Cyrus the Persian could serve as the Lords anointed (Isaiah 44:28, 45:1). One god stood behind all the worlds history.
