David Aberbach writes: 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