The political status of Jews in the Middle Ages, essentially subordinate to the Christian and Muslim authorities under whom they lived, combined with the continuing illegality of conversion to Judaism to prevent many conversions.
There were a wide variety of legal prohibitions that supplemented those imposed earlier. Between 395 and 408, the Byzantine Emperor Arcadius reenacted Constantius’ decrees prohibiting proselytizing by the Jews; in 538 and 548, the Third and Fourth Councils of Orleans forbade Jews to proselytize; between 717 and 720, Omar II forbade Jews to seek converts among Muslims; and in 740, Egbert, the Archbishop of York, in England, forbade Christians to attend Jewish festivals. Under such circumstances, conversions continued on an individual basis, with mass conversions occurring only during those rare moments when the political status of the Jews was improved.
Conversion of Khazars Encourages Sense of Jewish Mission
Conversions occurred more frequently in the areas that were contiguous to Christian or Muslim rule, suggesting that conversion was, in part at least, a political strategy to resist the religious intrusion of Christianity or Islam. The two most famous cases of this are the conversion of Yusuf Dhu Nuwas, the King of Himyar (in what is currently Yemen) in the early part of the sixth century and the conversion of the Khazar royal house in the 720s.
Dhu Nuwas, attempting to achieve freedom from Christian Abyssinian rule, could not get the assistance he sought from Persia, and his Jewish kingdom did not survive. The Khazars were a Turkic people who lived between the Black and Caspian Seas in Southern Russia. Legend has it that King Bulan held a debate among speakers for Judaism, Islam, and Christianity and chose on the basis of what he heard to accept Judaism. It is more probable, however, that Jewish traders, travelers, and refugees introduced Judaism to the kingdom. Khazaria eventually fell, and some of its Jews went to Eastern Europe.
What is most important about the Khazars was their effect on medieval Jews. The rise of Christianity and Islam, following on the loss of sovereignty and the concomitant demise in any military or political power, had made Jews desperate for a theological explanation of their plight. The explanation that they would one day be justified when the messiah came and that in the meantime they would be judged by their adherence to the mitzvot [commandments] and not by temporal success had not yet fully seeped into the Jewish imagination.
Medieval Jews were still considering the possibility of revival; they were encouraged by the conversion of the Khazars precisely because it illustrated for them the attractiveness of Judaism and because the conversion was an exemplification of the Jewish mission to offer itself. It is no accident that Judah Halevi (c. 1075-1141) grasped onto this story of the Khazars when he sought a framework within which to explain Judaism. His classic work, Sefer ha-Kuzari, sees in the act of conversion the essence of the Jewish message and the Jewish mission.
There are a large number of individual cases of conversion all through the Middle Ages. Many converts were made from among servants. Some of the converts to Judaism were even Christian clerics. These converts were often forced to flee for their safety to Muslim-controlled lands, where, of course, it was not illegal for Christians to convert to Judaism.
That even individual cases are recorded, that they occurred in each generation, and that non-Jewish authorities continued to argue and regulate against conversions indicate that such conversions did persist and that Jews continued, carefully, to accept converts, perhaps in larger numbers than we know. The Jews, restricted as they were, continued to prize converts and to welcome them when they could.
Autonomy Replaces Conversion in the Face of Persecution and Legal Restrictions
But it is clear that conversion was affected not only by the persecutions and restrictions and by the successes of Christianity and Islam in winning converts, but also by the changing attitudes internal to Judaism. An interpretation of Jewish life must fit Jewish reality and Jewish needs. As the Middle Ages progressed, the most realistic Jewish political conclusion was that segregation was beneficial. Inside their own communities, Jews maintained a high degree of autonomy, which they understood as power.
The value of this autonomy in providing religious–and to some extent other–freedom was such that competing interpretations that endangered it were discouraged. The need for self-segregation brought a justifying ideology that emphasized passivity and focused solely on obeying mitzvot and expectantly waiting for the messiah rather than obeying these particulars of Judaism but also offering their religion to the gentiles. Such a narrowing of Judaism’s view was useful in providing both a justification for the current life of the Jews and a hope for their future life.
Additionally, the Christian persecutions provoked so much hostility that Jews became suspicious of all Christians, making it psychologically all the more difficult to offer Judaism to the very people who were identified with mocking Judaism and persecuting, forcibly converting, injuring, and even killing Jews. The idea of a mission to the gentiles became more and more repugnant.
Other reasons for Jewish universalism’s decline included:
1. Jews were viewed by many gentiles as guilty of and disavowed by God for deicide, a dispersed people to be feared or abused or shunned, not joined;
2. Jews wouldn’t adjust their rituals to make it easier to convert to Judaism; and
3. the Jews insisted on really persuading gentiles and having real motives for conversion so that, for instance, when the Jews were persecuted, they simply found it difficult to accept that gentiles sincerely wished to convert a persecuted people.
Opposition to conversion became the Jewish tradition. Persecution and understandable fear had turned a principal obligation of the Jewish covenantal relationship, the spreading of God’s sovereignty through offering Judaism, into an activity spurned by the Jews themselves. Such attitudes toward conversion transformed the self-understanding of the Jewish mission itself from the original one of being a light unto the nations to keeping the religious commandments and waiting for the messiah.
Missionary quiescence, like nationalistic quiescence, became the tradition. Judaism almost stopped being taught to gentiles and no serious tradition of teaching the Noahide laws ever was developed.