Christianity began as a movement within Second Temple Judaism, but the two religions gradually diverged over the first few centuries of the Christian Era, and the Christian movement perceived itself as distinct from the Jews by the fourth century. Historians continue to debate the dating of Christianity's emergence as a discrete religion apart from Judaism. Philip S. Alexander characterizes the question of when Christianity and Judaism parted company and went their separate ways as "one of those deceptively simple questions which should be approached with great care". According to historian Shaye J. D. Cohen, "the separation of Christianity from Judaism was a process, not an event", in which the church became "more and more gentile, and less and less Jewish". Conversely, various historical events have been proposed as definitive points of separation, including the Council of Jerusalem and the First Council of Nicaea.

Jewish Christians were the followers of a Jewish religious sect that emerged in Judea during the late Second Temple period. These Jews believed that Jesus was the prophesied Messiah and they continued their adherence to Jewish law. Jewish Christianity is the foundation of Early Christianity, which later developed into Catholic and Eastern Orthodox Christianity. Christianity started with Jewish eschatological expectations, and it developed into the worship of Jesus as the result of his earthly ministry, his crucifixion, and the post-crucifixion experiences of his followers. Modern scholars are engaged in an ongoing debate about the proper designation of Jesus' first followers. Many modern scholars believe that the term Jewish Christians is anachronistic given the fact that there is no consensus about the date of the birth of Christianity. Some modern scholars have suggested that the designations "Jewish believers in Jesus" and "Jewish followers of Jesus" better reflect the original context.