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.
Origins of Christianity
Several Jewish sects are known to have existed during the 1st century CE: the Essenes, Pharisees, Sadducees, Zealots, and Christians. After the destruction of the Second Temple in 70 CE, most of these sects vanished, but Christianity and the Pharisees survived, with Christianity gradually becoming a separate religion, and the Pharisees developing into Rabbinic Judaism, or simply Judaism. Rather than a sudden split, there was a slowly growing chasm between Christians and Jews in the 1st centuries, and it took centuries for a complete break to manifest.