I’m on record as saying that ancient people never argued that Jesus didn’t exist. And I stand by this point. External critics like Celsus did argue that the Christian story about Jesus was a myth, or mythic, but they never went the next step of denying the existence of a flesh-and-blood Galilean. It just did not occur to them. Thus ancient “mythicism” will always be different from its modern anti-Christian variety. But it is still important.
What I recently discovered is that external critics of Christianity were not the only ancient mythicists. There were Christian mythicists as well: Christians who said that the Jesus of other Christians was mythical. One such Christian was Marcion of Pontus. Of course we have to piece together Marcion’s views from the heresiologists. But in this case we have a surprisingly clear statement from Tertullian, Against Marcion 4.4.4
| Marcion per Antithesis suas arguit ut interpolatum a protectoribus Iudaismi ad concorporationem legis et prophetarum, quo etiam Christum inde confingerent | Marcion in his Antitheses argues that [his Gospel] was falsified by the defenders of Judaism to become one body with the Law and Prophets, and from this [falsification] they fictionally invent even Christ. |
I continue to be floored by this remark. If I’m reading it correctly, then in his Antitheses, Marcion accused his early catholic opponents of inventing a fictional Christ. They invented a fictional Christ by falsifying or interpolating Marcion’s own Gospel with a series of stories and sayings that fused it to the storyline and narrative world of the Hebrew Bible (the Law and Prophets). Mythic stories would include Christ’s virgin birth in a stable, his being visited by shepherds and angels, his circumcision at the Jewish Temple, his genealogy, his visit to the Temple as a twelve-year old boy—in short, most of the stories now found in canonical Luke chapters 1-3.
Now, I should be clear. Marcion was a Christian, a follower and worshiper of Christ. He himself did not think that the man Jesus was a myth. He did not deny that a real crucifixion happened, or a real Last Supper, or a real resurrection. But the material that was added to Marcion’s Gospel—all the so-called prophecies, the infancy narratives, the genealogies—that was pure myth.
What we see unfolding, in other words, is an intra-Christian debate. A Christian accuses other Christians of inventing a fictional Christ. This is what we might call “intra-Christian mythicism,” Christians saying to other Christians, “you got Jesus wrong—way wrong.” And it teaches us a lot about how early Christians viewed the process of Gospel creation. Celsus was not the only writer to think that the Gospels contained myths. Some Christians thought that as well.
Marcion and his followers proposed that these other Gospels had been created or edited for apologetic reasons—to deal with objections raised against Christianity as a newfangled faith. But these Gospels also included some purely invented material. For Marcion(ites), any material not in their original Gospel was seen, not just as uninspired and illegitimate, but as invented and false.
I find this quite fascinating, because this early Marcionite mythicism has the opposite purpose as modern atheistic mythicism. Modern mythicism aims, as far as I can tell, to delegitimate and even destroy Christianity—to kill it at the roots, so to speak. But ancient, Marcionite mythicism has the goal of preserving Christianity by purifying it of its own gospel myths, the myths which made Jesus into a Jewish messiah as opposed to a cosmic Christ. For Marcion, the cosmic Christ was the true historical Jesus, and the Jewish messiah was the myth.
For more reflection on Gospel myths, please check out my book, How the Gospels Became History: https://amzn.to/3xGi7EF (audio) ; https://amzn.to/3U5CXoH (hardcover)
M. David Litwa, Ph.D. 
Considering some of the other non-canonical infancy gospels (The Infancy Gospel of Thomas, for example…which exists in Ireland!), and whatever their actual dates might be in different cases, it is very understandable why varied factions or varieties of Christians in those early centuries might want to distance themselves from divergent views. It is amazing to me that incidents from The Infancy Gospel of Thomas have made it into mainstream films about the childhood of Jesus, often re-interpreted (e.g. Jesus’ resurrecting a friend who died while playing with him, but without the original text’s detail that Jesus also caused his death in the first place, and the memorable commentary of Joseph about his ostensible son, that “This child should not be let out-of-doors, for whoever angers him ends up dead!”).
I think there are other types of mythicism possible, though, amongst other types of people. I am not a Christian, nor am I an atheist, but I am skeptical about the existence of a historical Jesus at this point (and am certainly skeptical about most of the stories about Jesus in the canonical Gospels, much less the apocrypha!); but, I am also not bothered by the possibility that there may nonetheless be a theological or metaphysical reality–whether an egregore, or something else–which exists that can be called “Jesus” and to which much of what has been attributed to Jesus by various types of Christians does, in fact, exist, but perhaps not in the way that Christians have insisted Jesus must have existed and still exists. This leaves room for interpretations of Jesus via other theological and metaphysical systems/religions and philosophical viewpoints which would see Jesus as, for example, an avatar via Hinduism, a bodhisattva via different sorts of Buddhism, a kami via Shinto, and maybe even something like a minor Tirthankara via Jainism, amongst other possibilities (an Ascended Master via Theosophy and its derivatives, perhaps?).
Humans are both highly diverse and highly creative, and thus I think it behooves us (whether as academics or as regular people just getting by in the world) to consider that there will always be exceptions, interesting combinations, and other phenomena that will provide unconsidered variations and anomalies to any system we set up, particularly any that are highly dichotomous or binarist. (And, please understand, I’m not saying that you or your work are either of those things, and this is not a critique, it’s just an attempt to account for some further possibilities that are brought to light by my own example and existence, and those of others that may not be as well-represented corporately as either the larger movements of vocal atheism or different denominational forms of Christianity.)
I hope that makes sense. :)
thank you very much for your extensive insights. I hope you comment again.