Jewish groups in the postexilic and late antique periods held diverse and often incompatible views on the question of Gentile impurity, leading to diverse and often incompatible attitudes toward conversion and intermarriage. Despite the claims of some earlier scholars, the impurity most commonly associated with Gentiles was not, in the oldest sources, ritual. I have argued here that the ritual impurity laws of Lev 12–15 were not held to apply to Gentiles in biblical and Second Temple times, nor were Gentiles considered intrinsically ritually impure, though they were considered profane. Jewish-Gentile interaction was not seriously hampered by an alleged Gentile ritual impurity, and the motivation for various customs and laws surrounding Jewish-Gentile interaction in Second Temple and later rabbinic sources was not, as is often assumed, the fear of contracting ritual impurity by contact.
The types of impurity most consistently applied to Gentiles were moral and genealogical. All ancient Jewish sources — from the Bible to the Talmud — asserted that Gentiles no less than Israelites were capable of generating moral impurity through the commission of heinous deeds of idolatry and immorality. Unlike ritual impurity, moral impurity is not communicable to other persons and is not removed by rituals of purification (though the latter idea appears at Qumran). Also unlike ritual impurity, moral impurity does not arise from certain unavoidable natural process and is never intrinsic (even at Qumran). On the contrary, moral impurity, being conditioned on behavior, is entirely avoidable. Gentiles, no less than Israelites, are capable of refraining from those sinful acts that generate moral impurity. Thus, to the degree that the distinction between Jew and Gentile was perceived to be a moral distinction, to that degree the boundary between Jew and Gentile could be crossed as Gentiles abandoned idolatry and immorality and adopted the behavioral norms of Jewish culture and identity.
Genealogical purity as the distinguishing characteristic of Israelite identity is introduced by Ezra, the late fifth-century priest from Persian Babylonia. 1 Ezra democratizes the priestly requirement for genealogical purity and thus establishes an impermeable boundary between Jews and Gentiles. As two distinct seeds, one holy and the other profane, Gentiles and Jews are permanently and inescapably distinct. Gentiles cannot become Jews. Intermarriage is prohibited as a profanation of the holy seed, and those