In her book When Christians Were Jews, Paula Fredriksen argues that one cannot easily point to a historical moment when Christianity ceased to be a Jewish sect and became a wholly separate religion. Rather, the process of disentanglement was a protracted one, remaining incomplete into the 4th century. Noah Benjamin Bickart, in his review, points to a particularly original part of her argument:

Most scholars see a dichotomy between Paul’s letters on the one hand and Matthew’s gospel on the other. The former are usually understood as products of a thoroughly Gentile church, [centered in Syria], whereas the latter seems to speak to a decidedly Jewish, albeit Jesus-worshipping, group [based in Jerusalem]. But Fredriksen argues that there was no daylight between Paul and the early Jerusalem church. It was just the difference between those who lived in the Diaspora and those who lived in Judea—all these early Christians regarded themselves as Jews.

Jews, especially those outside of Judea, had long had to negotiate their status as members of the broader Roman world while standing apart from it. . . . Likewise, many Romans who were not ethnic Judeans were attracted to Jewish practices. Synagogues in Syria, Asia Minor, and elsewhere already had a class of adherents who worshipped the God of Israel without having been circumcised or obligated to observe the Sabbath. Paul’s insistence that these Gentiles need not undergo circumcision or follow the [laws of the Torah] was neither a rejection of the law for ethnic Judeans nor a radical shift in the audience of the Christian message.

As with other competing forms of 1st-century Judaism, the Temple’s destruction in 70 CE changed everything for early Christianity. The Jerusalem church, made up of many of Jesus’ earliest followers, went up in the same smoke as the Temple. In the ensuing centuries, the vast majority of Christians were Gentiles who imposed an anti-Jewish agenda on the events and texts of their past. Fredriksen peels away these later theological layers to present an early Christian community that was decidedly Jewish.