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.
Historical background of the New Testament
Historians seek to understand where Jesus and his followers fit among other Jewish factions at the time. According to the Jewish-Roman historian Flavius Josephus, the three parties in contemporary Judaism were the Pharisees, the Sadducees and the Essenes, the last of these three being apparently marginalized and in some cases retired to quasi-monastic communities. Josephus also speaks of a "Fourth Movement", "Zealots", "Lestai" or "Sicarii".
The Pharisees were a powerful force in 1st-century Judea. Early Christians shared several beliefs of the Pharisees, such as resurrection, retribution in the next world, angels, human freedom, and Divine Providence. After the fall of the Temple, the Pharisaic outlook was established in Rabbinic Judaism. Some scholars speculate that Jesus was himself a Pharisee. In Jesus' day, the two main schools of thought among the Pharisees were the House of Hillel, which had been founded by the eminent Tanna, Hillel the Elder, and the House of Shammai. Jesus' assertion of hypocrisy may have been directed against the stricter members of the House of Shammai, although he agreed with their teachings on divorce. Jesus also commented on the House of Hillel's teachings (Babylonian Talmud, Shabbat 31a) concerning the greatest commandment and the Golden Rule. Historians do not know whether there were Pharisees in Galilee during Jesus' life, or what they would have been like.