…close analysis of Palestinian sources reveals that Palestinian rabbis read the biblical record very differently from the way in which it was read by some Jewish groups in the Second Temple and early Christian periods. Paul and later Christian sources join Ezra, Jubilees, and other Second Temple sources in constructing a universal prohibition of mixed marriages on biblical authority. In Second Temple sources, the consecration of Abraham and his seed to God entailed the permanent separation of that seed from the seed of Gentiles. According to Jubilees, the prohibition against the intermingling of these distinct seeds may be found in the Torah (Lev. 18:21, 20:3), and punishment for its violation is death. This prohibition and its punishment is understood to stand behind Phineas’ zealous execution of Zimri – the former being hailed as a hero in Second Temple sources – and to motivate Malachi 2:11, as well as Ezra’s dissolution of and interdict against mixed marriages. For his part, Paul denounces mixed marriages on the basis of the general prohibition against conjoining the holy and the impure.
By contrast, Palestinian rabbis maintain that biblical prohibitions of intermarriage (Dt 7 and 23) are partial only. The Torah contains no universal prohibition of intermarriage, and efforts to identify a biblical source for such a prohibition are severely suppressed (see the rabbis’ reaction to interpretations of Lev 18:21). This is not to say that the Palestinian rabbis were immune to concerns about such unions. Like their Second Temple predecessors, the rabbis condemned interethnic sexual relations. Nevertheless, the prohibition of such unions is understood to be rabbinic only (whether the eighteen decrees of Hillel and Shammai, a ruling of the Hasmonean court, or an even older authority). The Palestinian rabbis do not consider sexual union with a Gentile to be a capital crime, and although the Mishnah acknowledges the right of zealots like Phineas to deliver summary justice, Palestinian amoraim clearly disapprove of such zeal and seek to limit its power.
Christine E. Hayes, Gentile Impurities and Jewish Identities: Intermarriage and Conversion from the Bible to the Talmud (Oxford: Oxford University Press, 2002), 157-158.