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.
Heresy in Orthodox Judaism
The Greek term ἁίρεσις originally denoted "division," "sect," "religious" or "philosophical party," and is applied by Josephus to the three Jewish sects: Sadducees, Pharisees, and Essenes. The specific rabbinical term for heresies, or religious divisions due to an illegitimate spirit, is מינים ("minim") (lit. "kinds [of belief]"; the singular מין ("min") (literally, "a kind") for heretic or Gnostic is coined idiomatically, like "goy" and "`Am ha-aretz"). An alternative term, אפיקורוס (Apiqoros/Apikoros), which may have a different status, and is often used for apostates who turned towards agnosticism or atheism, is derived from Epicurus and the philosophy of Epicureanism.