Historically, the mother’s religion or nationality didn’t matter. Patriarchs were not required to convert their female slaves to monotheism, nor is there any indication they did so. The Jewish tribes of Dan, Naphtali, Gad, and Asher derived from Rachel and Leah’s slave girls. Not only the concubines, but Rachel the matriarch was pagan for years after she gave birth to the forefathers. She stole her father Lavan’s idols upon her departure from his land. When did that happen?

Her slave girl Bilga gave birth to two children consequently, then Rachel delivered Yosef, and then Yaacov continued to shepherd Lavan’s flock for six years (Gen31:41). Arguably, between Bilga’s and Rachel’s births, Leah produced five more children. Legally, Bilga’s children were Rachel’s (Gen30:3). Yosef was at least six years old at the time of their departure. Dan and Naphtali were probably eleven and twelve, respectively. According to another calculation, Yaacov married Rachel in his fourteenth year with Lavan and then shepherded for another six years. That would make Dan and Naphtali four and five at the clan’s departure, and Yosef was probably about three, so that Lavan’s cattle had the time to “multiply greatly” after his birth.

In modern rabbinical practice, children above the age of three must convert separately from their mother. In the Torah, all Bilga-Rachel’s children were older at the time when Rachel reconfirmed her idolatry, but they are considered perfectly Jewish. It seems that Yaacov, too, practiced idolatry at the time, because Lavan was certain that Yaacov stole his idols (Gen31:30). Indeed, it’s hard to imagine that Lavan gave his two daughters to someone who would seem to him an atheist refusing to bow down to idols of the land. The midrashic explanation (Ber.r.74:4) that Rachel stole the idols in order to dissuade her father from their worship is not credible: he would have replaced them with other idols. Besides, during their ten days of marching from Lavan (Gen31:22-23) Rachel had plenty of time to dispose of the idols rather than risk violent confrontation with Lavan—and presumably with Yaacov—over them.

The rule of maternal lineage originally expanded Jewishness. At the time the rule was promulgated, children of Jewish fathers were definitely Jewish; even if their mother was pagan, she was automatically converted at marriage. Jewish women, likewise, lost their religion when marrying pagans; marriage was only religious, thus these Jewish women passed through pagan rites at marriage. Their children did not adhere to Judaism. Even so, sages pronounced those children Jewish. The rule means that even children of Jewish mothers are Jewish, all the more so children of Jewish fathers. Now the rule of maternal lineage disqualifies children of Jewish fathers and Gentile mothers; that is contrary to the sages’ intention.

Indeed, even now—in theory—Jewishness is patrilinear: children of properly married Jewish fathers are always Jewish. Here is the trick: in order to be married properly, a Jewish man should have his non-Jewish spouse converted and perform a religious marriage ceremony. If, however, we adopt the prevailing law of the land on secular marriages, then the unquestionable patrilinear descent prevails.

The rule of maternal lineage became counterproductive. It allowed Jewish women to marry Gentiles without reserve. Whomever they marry, whatever life they live, their children are Jewish. That’s empirically untrue. Children of Jewish mothers and Gentile fathers rarely feel themselves Jewish; the paternal influence on family upbringing is stronger than the maternal. On the contrary, children of Jewish fathers and whatever mothers very often associate themselves with Jewish people; Jewish fathers often emphasize Jewishness before their children to offset the maternal Gentile influence. At a minimum, fathers clearly exert a stronger influence on male children than mothers. Wives often eagerly succumb to their husbands’ beliefs; it is common knowledge that Gentile wives of unobservant Jews are often closer to Judaism and Jewish culture than their Jewish spouses.

This is, indeed, what the Talmud says. Yevamot 23a comments on Deut7:4: “For it/he will turn your son away from me.” The reading “it” makes perfect sense: the foreign people with whom the Jews intermarry turns them away from God. The sages, however, preferred the reading “he” which made the interpretation torturous. “He will turn your son away” smacks of homosexual couples. The rabbis devised an ingenuous explanation: he (the foreign husband of a Jewish woman) will turn away your grandson (his son). The Torah routinely employs the word son to mean “descendant.” From that, the sages concluded that a foreign husband’s son is “your son,” and Jewish, and therefore Jewishness is maternal. But no, the Torah is explicit: he will turn your [grand]son away; there is no probability or ambiguity here. Grandchildren of mixed families with a Gentile father are always non-Jewish. It makes little sense to argue with rabbis whether the children of Jewish women and Gentile men are Jewish; what is important is that the Torah explicitly pronounces their grandchildren non-Jewish—and that’s empirically true.

The rigid rabbinical demand that prospective converts are only driven by the desire to embrace Judaism is historically unwarranted. Jewish men took—and converted—foreign wives in great numbers who would otherwise not have considered embracing Judaism.

Gender-blind inheritance of Jewishness means that a person can be Jewish even if he or she has only a remote Jewish ancestor. There is no need for a direct maternal line: in each generation, the spark of Jewishness is transmitted through any parent. The whole world (well, the nations among whom the Jews have lived) can recognize itself as Jewish. Any descendant of a Jew is potentially a Jew. He can claim his Jewishness and return to Judaism.