Marcionism was denounced by its opponents as heresy, and written against, notably by Tertullian, in a five-book treatise Adversus Marcionem, written about 208. However, the strictures against Marcionism predate the authority, claimed by the First Council of Nicaea in 325, to declare what is heretical against the Church. Marcion's writings are lost, though they were widely read and numerous manuscripts must have existed. Even so, many scholars (including Henry Wace) claim it is possible to reconstruct and deduce a large part of ancient Marcionism through what later critics, especially Tertullian, said concerning Marcion.
According to Tertullian and other writers of the mainstream Church, the movement known as Marcionism began with the teachings and excommunication of Marcion from the Church of Rome around 144. Marcion was reportedly a wealthy shipowner, the son of a bishop of Sinope of Pontus, Asia Minor. He arrived in Rome circa 140, soon after Bar Kokhba's revolt. That revolution, along with other Jewish-Roman wars (the Great Jewish Revolt and the Kitos War), provides some of the historical context of the founding of Marcionism. Marcion was excommunicated from the Roman Church because he was threatening to make schisms in the church.
Marcion used his personal wealth, (particularly a donation returned to him by the Church of Rome after he was excommunicated), to fund an ecclesiastical organization. Marcionism continued in the West for 300 years, although Marcionistic ideas persisted much longer.
The organization continued in the East for some centuries later, particularly outside the Byzantine Empire in areas which later would be dominated by Manichaeism. This is no accident: Mani is believed to have been a Mandaean, and Mandaeanism is related to Marcionism in several ways. For example, both Mandaeanism and Marcionism are characterized by a belief in a Demiurge. The Marcionite organization itself is today extinct, although Mandaeanism is not.
The premise of Marcionism is that many of the teachings of Christ are incompatible with the actions of Yahweh, the God of the Old Testament. Tertullian claimed Marcion was the first to separate the New Testament from the Old Testament. Focusing on the Pauline traditions of the Gospel, Marcion felt that all other conceptions of the Gospel, and especially any association with the Old Testament religion, was opposed to, and a backsliding from, the truth. He further regarded the arguments of Paul regarding law and gospel, wrath and grace, works and faith, flesh and spirit, sin and righteousness, death and life, as the essence of religious truth. He ascribed these aspects and characteristics as two principles, the righteous and wrathful god of the Old Testament, who is at the same time identical with the creator of the world, and a second God of the Gospel, quite unknown before Christ, who is only love and mercy. Marcion is said to have gathered scriptures from Jewish tradition, and juxtaposed these against the sayings and teachings of Jesus in a work entitled the Antithesis. Besides the Antithesis, the Testament of the Marcionites was also composed of a Gospel of Christ which was Marcion's version of Luke, and that the Marcionites attributed to Paul, that was different in a number of ways from the version that is now regarded as canonical. It seems to have lacked all prophecies of Christ's coming, as well as the Infancy account, the baptism, and the verses were more terse in general. It also included ten of the Pauline Epistles (but not the Pastoral Epistles or the Epistle to the Hebrews, and, according to the Muratonian canon, included a Marcionite Paul's epistle to the Alexandrians and an epistle to the Laodiceans) In bringing together these texts, Marcion redacted what is perhaps the first New Testament canon on record, which he called the Gospel and the Apostolikon, which reflects his belief the writings reflect the apostle Paul and Jesus.
Marcionites hold maltheistic views of the god of the Hebrew Bible (known to some Gnostics as Yaltabaoth), that he was inconsistent, jealous, wrathful and genocidal, and that the material world he created is defective, a place of suffering; the god who made such a world is a bungling or malicious demiurge. "In the god of the [Old Testament] he saw a being whose character was stern justice, and therefore anger, contentiousness and unmercifulness. The law which rules nature and man appeared to him to accord with the characteristics of this god and the kind of law revealed by him, and therefore it seemed credible to him that this god is the creator and lord of the world (κοσμοκράτωρ). As the law which governs the world is inflexible and yet, on the other hand, full of contradictions, just and again brutal, and as the law of the Old Testament exhibits the same features, so the god of creation was to Marcion a being who united in himself the whole gradations of attributes from justice to malevolence, from obstinacy to inconsistency. In Marcionite belief, Christ is not a Jewish Messiah, but a spiritual entity that was sent by the Monad to reveal the truth about existence, and thus allowing humanity to escape the earthly trap of the demiurge. Marcion called God, the Stranger God, or the Alien God, in some translations, as this deity had not had any previous interactions with the world, and was wholly unknown.
It was no mere school for the learned, disclosed no mysteries for the privileged, but sought to lay the foundation of the Christian community on the pure gospel, the authentic institutes of Christ. The pure gospel, however, Marcion found to be everywhere more or less corrupted and mutilated in the Christian circles of his time. His undertaking thus resolved itself into a reformation of Christendom. This reformation was to deliver Christendom from false Jewish doctrines by restoring the Pauline conception of the gospel, Paul being, according to Marcion, the only apostle who had rightly understood the new message of salvation as delivered by Christ. In Marcion's own view, therefore, the founding of his church—to which he was first driven by opposition—amounts to a reformation of Christendom through a return to the gospel of Christ and to Paul; nothing was to be accepted beyond that. This of itself shows that it is a mistake to reckon Marcion among the Gnostics. A dualist he certainly was, but he was not a Gnostic.
Marcionism shows the influence of Hellenistic philosophy on Christianity, and presents a moral critique of the Old Testament from the standpoint of Platonism. According to Harnack, the sect may have led other Christians to introduce a formal statement of beliefs into their liturgy (see Creed) and to formulate a canon of authoritative Scripture of their own, thus eventually producing the current canon of the New Testament. "As for the main question, however, whether he knew of, or assumes the existence of, a written New Testament of the Church in any sense whatever, in this case an affirmatory answer is most improbable, because if this were so he would have been compelled to make a direct attack upon the New Testament of the Church, and if such an attack had been made we should have heard of it from Tertullian. Marcion, on the contrary, treats the Catholic Church as one that 'follows the Testament of the Creator-God,' and directs the full force of his attack against this Testament and against the falsification of the Gospel and of the Pauline Epistles. His polemic would necessarily have been much less simple if he had been opposed to a Church which, by possessing a New Testament side by side with the Old Testament, had ipso facto placed the latter under the shelter of the former. In fact Marcion’s position towards the Catholic Church is intelligible, in the full force of its simplicity, only under the supposition that the Church had not yet in her hand any 'litera scripta Novi Testamenti.'
In Lost Christianities, Bart Ehrman contrasts the Marcionites with the Ebionites as polar ends of a spectrum with regard to the Old Testament. Ehrman acknowledges many of Marcion's ideas are very close to what is known today as "Gnosticism", especially its rejection of the Jewish God, the Old Testament, and the material world, and his elevation of Paul as the primary apostle. In the PBS documentary, From Jesus to Christ, narrated by Elaine Pagels, Ehrman, Karen King, and other secular New Testament scholars, Marcion's role in the formation of the New Testament canon is discussed as pivotal, and the first to explicitly state it. There were early Christian groups, such as the Ebionites, that did not accept Paul as part of their canon.
Robert M. Price, a New Testament scholar at Drew University, considers the Pauline canon problem: how, when, and who collected Paul's epistles to the various churches as a single collection of epistles. The evidence that the early church fathers, such as Clement, knew of the Pauline epistles is unclear. Price investigates several historical scenarios and comes to the conclusion and identifies Marcion as the first person known in recorded history to collect Paul's writings to various churches together as a canon, the Pauline epistles. Robert Price summarizes, "But the first collector of the Pauline Epistles had been Marcion. No one else we know of would be a good candidate, certainly not the essentially fictive Luke, Timothy, and Onesimus. And Marcion, as Burkitt and Bauer show, fills the bill perfectly. If this is correct, then Marcion's role in the formation and development of Christianity is pivotal.
The story proceeds to say that he asked the Roman presbyters to explain the texts, "A good tree cannot bring forth evil fruit," and "No man putteth a piece of new cloth unto an old garment," texts from which he himself deduced that works in which evil is to be found could not proceed from the good God, and that the Christian dispensation could have nothing in common with the Jewish. Rejecting the explanation offered him by the presbyters, he broke off the interview with a threat to make a schism in their church.
Tertullian, along with Epiphanius of Salamis, also charged that Marcion set aside the gospels of Matthew, Mark and John, and used Luke alone. Tertullian cited Luke 6:43-45 (a good tree does not produce bad fruit) and Luke 5:36-38 (nobody tears a piece from a new garment to patch an old garment or puts new wine in old wineskins), in theorizing that Marcion set about to recover the authentic teachings of Jesus. Irenaeus claimed, "[Marcion's] salvation will be the attainment only of those souls which had learned his doctrine; while the body, as having been taken from the earth, is incapable of sharing in salvation. Tertullian also attacked this view in De Carne Christi.
Hippolytus reported that Marcion's phantasmal (and Docetist) Christ was "revealed as a man, though not a man", and did not really die on the cross. However, Ernest Evans, in editing this work, observes:
This may not have been Marcion's own belief. It was certainly that of Hermogenes (cf. Tertullian, Adversus Hermogenem) and probably other gnostics and Marcionites, who held that the intractability of this matter explains the world's many imperfections.
Because of the rejection of the Old Testament which originates in the Jewish Bible, the Marcionites are believed by some Christians to be anti-Semitic. Indeed, the word Marcionism is sometimes used in modern times to refer to anti-Jewish tendencies in Christian churches, especially when such tendencies are thought to be surviving residues of ancient Marcionism. For example, on its web site, the Tawahedo Church of Ethiopia claims to be the only Christian church that is fully free of Marcionism. On the other hand, Marcion did not claim Christians to be the New Israel of Supersessionism, and did not try to use the Hebrew scriptures to support his views. Marcion himself does not appear to be anti-Semitic, rather he rejected Jewish scriptures as irrelevant.
The Prologues to the Pauline Epistles (which are not a part of the text, but short introductory sentences as one might find in modern study Bibles ), found in several older Latin codices, are now widely believed to have been written by Marcion or one of his followers. Harnack notes : "We have indeed long known that Marcionite readings found their way into the ecclesiastical text of the Pauline Epistles, but now for seven years we have known that Churches actually accepted the Marcionite prefaces to the Pauline Epistles! De Bruyne has made one of the finest discoveries of later days in proving that those prefaces, which we read first in Codex Fuldensis and then in numbers of later manuscripts, are Marcionite, and that the Churches had not noticed the cloven hoof.". Conversely, several early Latin codices contain Anti-Marcionite prologues to the Gospels.
Marcion is believed to have imposed a severe morality on his followers, some of whom suffered in the persecutions. In particular, he refused to re-admit those who recanted their faith under Roman persecution. Others of his followers, such as Apelles, created their own sects with variant teachings.
Many atheists, agnostics, and secular humanists agree with Marcion's examples of Bible atrocities, and cite the same passages of the Old Testament to discredit Christianity and Judaism. Most Christians agree with Marcion that the Old Testament's alleged approval of genocide and murder are inappropriate models to follow today. Some Christian scholars, such as Gleason Archer and Norman Geisler, have dedicated much of their time to the attempt to resolve these perceived difficulties, while others have argued that just punishments (divine or human), even capital punishments, are not genocide or murder because murder and genocide are unjustified by definition (see Christian Reconstructionism).
William Blake's spiritual beliefs, as evidenced in Songs of Experience (1794), in which he distinguishes between the Old Testament God, whose restrictions he rejected, and the New Testament God (Jesus Christ in Trinitarianism), whom he saw as a positive influence.
For some, the alleged problems of the Old Testament, and the appeal of Jesus are such that they identify themselves as modern day Marcionites, and follow his solution in keeping the New Testament as sacred scripture, and rejecting the Old Testament canon and practices. Carroll R. Bierbower is a pastor of a church he says is Marcionite in theology and practice. The Cathar movement, historically and in modern times, reject the Old Testament for the reasons Marcion enunciated. It remains unclear whether the 11th century Cathar movement is in continuation of earlier Gnostic and Marcion streams, or represents an independent re-invention. John Lindell, a former Methodist and Unitarian Universalist pastor, advocates Christian deism, which does not include the Old Testament as part of its theology.
Recently, feminist biblical scholar Amy-Jill Levine identified Marcion thought in liberation theology and in the World Council of Churches in her book, "The Misunderstood Jew: The Church and the Scandal of the Jewish Jesus". An Orthodox Jew, she regards Marcionism as an antisemitic heresy that is alive and present in Christianity today and a serious obstacle towards greater Christian-Jewish understanding.