The unprecedented growth of Islam in the West, despite prejudice and hatred, contrasts with the demographic stagnation of the Jewish people - several million fewer now than in 1939. Conversion to practically every other religion remains considerably easier than conversion to Judaism. Why is traditional conversion to Judaism so hard?
There is a close link between Tishah b'Av, the anniversary of the destruction of the Temple in Jerusalem in 70 CE, and rabbinic discouragement of gentiles from conversion after the Roman-Jewish wars (66-70, 115-17, 132-35 CE). Roman concern with Jewish conversion began prior to the destruction of the Temple. Though not a missionary religion (early Christians such as Paul, Barnabas and Peter are the only first-century Jewish missionaries known by name), pre-70 Judaism was highly varied and expanding in the Roman empire. It attracted sympathisers and adherents among the underprivileged, powerless, persecuted classes of the empire, especially slaves and women.
The Oxford scholar, Martin Goodman has written that conversion to Judaism was unique in the ancient world as converts were accepted as equals by Jews.
Many spiritually hungry pagans, drawn to Judaism by its moral code, its valuation of human life and charity, and hope of messianic salvation, adopted Jewish customs, particularly the Sabbath and the dietary laws; but Judaism spread also among upper-class Romans. Privileges granted to the Jews by Julius Caesar encouraged proselytisation: freedom from emperor worship and army service as well as the right to congregate as a religious group. According to the historian, Louis Feldman, conversion was the single most important issue on which the emperors legislated in the entire history of Roman-Jewish relations.
The Midrash takes pride in legends that famous Romans such as Nero converted to Judaism. Some of the most eminent talmudic rabbis, including Rabbi Akiva and Rabbi Meir, were allegedly descended from converts; their Jewishness was not questioned. In any case, many biblical characters, including the children of Moses and Solomon, were born to foreign women. Acceptance of Judaism was a private matter for the convert, not a public process fixed by religious authorities. The Temple was a site of pilgrimage and sacrifice not just for Jews but also for many others who were drawn to Jewish religious and national distinctiveness.
Prior to the destruction of the Temple, there seems to have been no unified standard of conversion, no refusal to accept conversions or prolongation of the process. On the contrary, the often-violent rivalry between Judaism and Greco-Roman culture meant that conversion to Judaism could be seen as a sign of its superiority.
Judaism reached the peak of its expansion in the years prior to the 66 CE revolt. Salo Baron, in his monumental A Social and Religious History of the Jews, points out that the Jews - comprising as many as 10 percent of the Western Roman empire and 20 percent of the Eastern Roman empire - were seen by Rome as a threat to the unity of the Roman empire, whose universal culture was Greek, not Jewish. Too-rapid expansion, concludes Baron, had endangered Judaism, for it had "made too many compromises, and flirted with too many alien ways of life and thought. The results were those sharp sectarian and political divisions which had almost brought it to the brink of extinction."
The Roman-Jewish wars led to depopulation of Jews both in the Land of Israel and in the diaspora and transformed the Jews into a homeless, persecuted, semi-pariah people until the modern period.
The Jewish perception of conversion changed as the forces which brought about the expansion of Judaism also contributed to Greco-Roman antisemitism and, ultimately, the destruction of the Jewish state.
After the final, disastrous Jewish war against Rome, the Bar Kochba revolt (132-5 CE), Jewish leaders were no longer kings and politicians, Temple priests and messianic warriors, but rabbis dedicated to the survival of the Jewish people and Judaism in the Roman empire. The Romans approved organised rabbinic authority as the rabbis regarded Torah study - not proselytisation and anti-Roman messianic militancy - as the highest good, essential to Jewish survival.
The rabbis dealt with the Roman ban on Jewish proselytisation and the continued attraction of Judaism by making the process of conversion harder and warning of the hazards of Judaism: "What is your motive?" they would ask the prospective convert. "Don't you know that Israel is suffering, persecuted, oppressed, harassed and beaten down with a multitude of sorrows?"
The Talmud tells of a nephew of Titus, destroyer of the Temple, who raises Titus from the dead to ask if he should convert to Judaism: "Their laws are so hard," Titus replies, "You won't be able to keep them."
Judaism survived by turning inward, strengthening its laws and customs, retaining its universalist outlook but leaving missionary monotheism to Christianity and, later, Islam. Only since the French Revolution and the Napoleonic wars, when German Reform began, has Judaism regained some of its variety, and become again attractive to converts. Yet, the memory of national vulnerability survives in Tishah b'Av - together with ancient wariness of conversion. Tishah b'Av reminds us that communal disunity and strife can be fatal, and converts might justly be warned as in the past: Judaism remains a target for antisemites, and Jews continue to suffer vilification, though not on the scale of the past.