In the first century Judaism existed in two geographical areas, with such distinct features as to lead some scholars to talk, with some exaggeration, of two types of religion. On the one hand, Palestinian Judaism, better called Rabbinic Judaism because both Palestine and Babylonia constituted its homeland, took over the tradition of the Pharisees after 70 when the rabbis emerged as a distinctive group. The leader of the rabbis was the patriarch, with the school and the judicial court as the major rabbinic institutions. As a group the rabbis concentrated on biblical interpretation in the form of Midrash, emphasizing first of all legal discussions (halakhah), secondarily ethical teachings and stories about biblical or rabbinic figures (aggadah). Aramaic and then Hebrew were the languages used, but some Greek influence and knowledge of the language are also discernible (e.g., the historian Josephus could write Greek). By the end of the first century, some 2 million Jews lived in Palestine itself.
On the other hand, Diaspora Judaism, found since 586 in Egypt, Asia Minor, Syria, Cyrene, and Greece, attempted an interpretation of the biblical tradition for Greek-speaking Jews. Naturally it showed a higher degree of assimilation to Greek culture and thought than did Palestinian Judaism. We know very little about the kind of communication that went on between those two Jewish groups. It appears that Second Temple Judaism saw Jews thrive in major places around the Mediterranean basin and in the Near East (there were about 4 million Jews in the empire toward the end of the first century, i.e., 7 percent of the total population; they made up one-third of the population in Alexandria), constituting an eastern and a western Diaspora. The evidence shows that Judaism was an attractive religious alternative for many and enjoyed an extraordinary success in proselytism. Repeated influx of exiles from Palestine, however, led to a gradual hebraizing of the Greek-speaking synagogue and to the spread of tannaitic Judaism in the Diaspora.After 120 C.E., the Greek-speaking Diaspora entered a period of decline. Babylonian Jews had already turned to Aramaic; more rabbis from the land of Israel took residence in Babylonia after 135 and made Rabbinic Judaism flourish. Elsewhere Hellenistic Christianity absorbed most of the Gentiles who had been attracted to Judaism (proselytes who had converted to Judaism and God-fearers or sympathizers who had adopted some Jewish practices only), as well as a fair number of Hellenized Jews, perhaps already drawn to Greek mysteries. Hellenistic Judaism finally withered away for lack of survival power. Features common to both Rabbinic and Diaspora Judaism must not be overlooked. For both the law of Moses with its essential demands retained undisputed primacy; both were submitted to Hellenistic influences, although they yielded to various degrees of assimilation to Greek culture.