Stark, Rodney. "Chapter 3: The Mission to the Jews: Why It Probably Succeeded." The Rise of Christianity: How the Obscure, Marginal Jesus Movement Became the Dominant Religious Force in the Western World in a Few Centuries. San Francisco: Harper Collins, 1997, 49-71.
Stark readily admits that the earliest Christians were centered around the synagogue. However, sometime around the revolt in 66-74 the focus shifted away from the Jewish world. Stak, going against the weight of much scholarship, suggests "that not only was it the Jews of the diaspora who provided the initial basis for church growth during the first and early second centuries, but that Jews continued as a significant source of Christian converts until at least as late as the fourth century and that Jewish Christianity was still significant in the fifth century" (Stark 1997, 49). He makes this claim based on several sociological steps, coming to a conclusion that we do not know of a blanket rejection of Christianity among Jews, and that the demographics suggest there were thriving Jewish Christian communities.
Stark asks how we know that Jews didn't convert to Christianity. There remained large groups of Jews even into the fifth century (and beyond). Written sources from Christian and Jewish sources speak negatively of those on the other side (Stark 1997, 50). Aside from that, Stark finds no evidence of mass conversion or mass rejection.
One reason people have assumed a "melting pot" has not happened is that there are ethnic enclaves in large cities. However, Stark notes, this does not mean that assimilation, akin to conversion, doesn't happen. It merely says that assimilation does not happen all the time (Stark 1997, 51). Likewise, the presence of synagogues in the fourth century only means that not all Jews became Christians. Motion of emancipated Jews in the 19th century effectively removed some Jews from the recognizable forms of Judaism but did not necessarily imply conversion (Stark 1997, 52). Some certainly converted to escape the minority group. But this cannot be assumed in every case. Stak suggests that Jewish people who became secularized due to rejection of their ethnic communities would be highly likely to covert to a new religion, especially one like Christianity, which had some forms familiar to them (Stark 1997, 55). Further, the social networks which already existed could be predicted to draw others into the Christian faith (Stark 1997, 56).
Stark considers the population of Hellenized Jews in the Diaspora in the first century to have been from four to six million (Stark 1997, 57). They were known as prosperous people but they drifted from some indicators of loyalty to the faith, such as use of Hebrew. The Christian faith may have been attractive in part due to its continuity with Judaism as well as its accommodation of cultural differences (Stark 1997, 59). As an example of accommodation, Stark notes Philo's attempts at "reasonable" explanations of the requirements of the Torah (Stark 1997, 60).
Stark suggest that social networks were instrumental in the spread of Christianity among Hellenized Jews. They were already accustomed to receiving teachers from Jerusalem. They had connections with family and friends. They may have been relatively likely to receive Christian teaching (Stark 1997, 62). Stark finds suggestions that this very thing happened. Many converts seem to be Hellenized jews. The New Testament largely assumes some knowledge of the Septuagint. Teaching happened in synagogues. Churches were located in the Jewish parts of cities (Stark 1997, 63). Stark also notes the Jewish social structure may have been operative in the resistance to Marcion's attempts to remove the Old Testament from Christianity (Stark 1997, 65).
In light of this information, Stark suggests we may do well to see the criticisms of Judaism as an attempt to temper Christianity and move it away from extreme dependence on Jewish forms (Stark 1997, 66). Stark closes his chapter by observing that there are extensive archaeological remains indicating Jewish and Crhsitian communities mixed and compatible in many customs of living and burial up to the seventh century (Stark 1997, 68).