The concept of “conversion” as such does not appear in the Hebrew Bible. We associate conversion with “religion,” a term used to describe certain human experiences and behaviors; but in the worldview of the Hebrew Bible’s authors, the word “religion” would have been foreign. Collective identity, kinship, and shared traditions (notions commonly associated with “ethnicity” or “peoplehood”) were not separable from ideas about the divine.
Israelites do not appear to have sought out others to join their covenant with God, nor are they commanded to do so. Conversely, Israelite fear or honor of others’ gods are characterized as covenantal violations akin to adultery, not as “conversion.”
That said, most biblical writers take it for granted that “outsiders” can be incorporated into their populace (including its worship and common lines of descent) through marriage, bondage, alliance, residency, adoption, and the like. In addition, prophets such as Isaiah and Zechariah envision a desirable future in which many peoples come to embrace Yahweh, the god of Israel, and worship at the temple in Jerusalem.
The writers of Genesis and Exodus, for example, betray no concern about the status of Joseph’s wife, Asenath, daughter of an Egyptian priest and mother to Ephraim and Manasseh (Gen 41:45-52), nor about Moses’s wife, Zipporah, daughter of a Midianite priest (Exod 2:16-21), who performs their son’s circumcision (Exod 4:25-26). The “perpetual exclusion” of Ammonites and Moabites from the “congregation of the Lord” commanded in Deut 23:3-4 likewise presumes an openness to the inclusion of other “others.” Males enslaved to Israelites are commanded to be circumcised and to partake in the Passover meal; both these acts mark membership in the Israelite covenant community (Gen 17:10-14, Exod 12:44, Exod 12:48).
In later books of the Hebrew Bible, the incorporation of “outsiders” becomes both more explicit and more contentious. Ezra and Nehemiah, in particular, forbid the inclusion even of people not excluded elsewhere, whereas other books—in particular, Ruth and the apocryphal Judith—explicitly reject Ezra’s innovations and the exclusions demanded by Deuteronomy.
Ruth the Moabite is joined by marriage to an Israelite household in Moab and, after being widowed, marries a “redeeming kinsman,” Boaz, in Bethlehem—with whom she becomes part of the line of King David. More explicitly, Ruth joins herself to the Israelite Naomi—and to her land, people, and god—through a stirring oath that underscores the interconnection among these three elements of Israelite identity (Ruth 1:16-17).
In the book of Judith, Achior the Ammonite appears as an enemy mercenary who nonetheless extols the power and righteousness of God as he recites a capsule history of Israelite origins, exodus, conquest, exile, and restoration (Jdt 5:5-21). After the heroine Judith assassinates the Assyrian general Holofernes—casting his army into disarray and precipitating their defeat—it is reported that when the now-captive Achior “saw all that the God of Israel had done, he believed firmly in God. So he was circumcised, and joined the house of Israel, remaining so to this day” (Jdt 14:10).
Some scholars insist that such a change in personal “belief” as is attributed to Achior, but not to Ruth, determines “conversion.” If so, then “conversion” is not found in the Hebrew Bible, though it is found in the Apocrypha. Yet, when biblical culture is examined on its own terms, every generation of Israelites may be seen to include those neither born nor raised in—but nonetheless joined to—the house of Israel.