Marcionism is an ancient heresy that goes back to the 2nd Century AD. It is named after its founder, Macion of Sinope. Marcion believed that Christ was the Savior of mankind, but he asserted that the deity of the Old Testament was a different god than that of the New Testament, who was a higher, more noble deity. M
arcionism is a subset of Gnosticism (Marcion believed that Christ was sent not by the God of the Old Testament, but by the Monad – a Gnostic concept), and similarly held to spiritual dualism. Marcionism rejects the Old Testament en totalis, and denies that it is authoritative Holy Writ. Marcionism was judged a heresy by Tertullian in 203 AD. Whereas Gnostics affirmed their doctrines through asserting hidden or secret knowledge, Marcion affirmed their (very similar) doctrines by a canon of 10 Gospels and 9 Pauline Epistles.
Marcionism seems to have waned by the 5th Century AD, although he is widely quoted by modern enemies of the faith, including German Nazis and Bart Erhman. Certain individuals who hold to the designation “New Testament Christians” or “Red Letter Christians” are inadvertently holding to Marcionism.