Was Jesus the Founder of Christianity?
However one chooses to fit Jesus into the mosaic of first-century Judaism, faith in Jesus is Jewish at its root. We say “faith in Jesus” because while followers of Jesus were called “Christians” in the first few centuries of their belief, it is incorrect to call the faith “Christianity” — a label that did not emerge until later.
As Reform rabbi Evan Moffic puts it, “Jesus did not start Christianity. Jesus lived and died as a Jew. Christianity emerged after his death as an off-shoot of Judaism, eventually separating and becoming its own religion. The beliefs and practices of this religion differ from Judaism, but they remain rooted in it.”
Jesus shared much in common with other Jews of his day, though he also differed from them. As a Jew, he had a bris; he had the first-century equivalent of a pidyon ha-ben ceremony a month after his birth; he observed Passover. He was in Jerusalem for Sukkot and was at the Temple during Hanukkah. He customarily attended synagogue, and on at least one occasion, was invited up to speak on what today would be known as the Haftarah. In his teachings, he emphasized Jewish values such as kibud av va’em (honor of parents) and tzedakah (charity).
Yet Jesus took issue with certain Jewish traditions and with some Pharisees and Sadducees. That is why some have wryly referred to Jesus as the “first Reform Jew.” He healed people on the Sabbath when others considered healing inappropriate for the day of rest. He spoke and taught with an authority no other rabbi dared to claim. All of these disputes, however, took place within first-century Judaism. Scholars and theologians debate the particular kind of Judaism Jesus represented, but it was Judaism nonetheless. There was, as yet, nothing called “Christianity.”
Was Jesus, then, the founder of a new, non-Jewish religion? No, he was not. For in one encounter, a Samaritan woman said to him, “’I know that Messiah is coming. When he comes, he will tell us all things.’ Jesus replied, ‘I who speak to you am he’” (John 4:25–26).
 Rabbi Evan Moffic, What Every Christian Needs to Know About the Jewishness of Jesus: A New Way of Seeing the Most Influential Rabbi in History (Nashville: Abingdon Press, 2015), xi.