Judaism
Christianity was originally a sect of Second Temple Judaism, but the two religions diverged in the first century. The differences between Christianity and Judaism originally centered on whether Jesus was the Jewish Messiah but eventually became irreconcilable. Major differences between the two faiths include the nature of the Messiah, of atonement and sin, the status of God's commandments to Israel, and perhaps most significantly of the nature of God himself. Due to these differences, Judaism traditionally regards Christianity as Shituf or worship of the God of Israel which is not monotheistic. Christianity has traditionally regarded Judaism as obsolete with the invention of Christianity and Jews as a people replaced by the Church, though a Christian belief in dual-covenant theology emerged as a phenomenon following Christian reflection on how their theology influenced the Nazi Holocaust.
Split of Christianity and Judaism
Most of Jesus's teachings were intelligible and acceptable in terms of Second Temple Judaism; what set Christians apart from Jews was their faith in Christ as the resurrected messiah. While Christianity acknowledges only one ultimate Messiah, Judaism can be said to hold to a concept of multiple messiahs. The two most relevant are the Messiah ben Joseph and the traditional Messiah ben David. Some scholars have argued that the idea of two messiahs, one suffering and the second fulfilling the traditional messianic role, was normative to ancient Judaism, predating Jesus. Jesus would have been viewed by many as one or both.