Our interest is to figure out a tradition and principally the Marcionite tradition because it is probably the oldest Christian tradition. The Marcionites did not believe that Jesus was a human being. There were of course a whole bunch of heretical groups which shared this understanding - but who knows how many people were actually 'into' this stuff. Maybe one hundred believers, maybe a thousand. Who knows.
The point is that the Marcionites were a big Church. Whenever the pagan critic Celsus wrote his influential anti-Christian treatise, ᾽Αληθής λόγος (140 - 177 CE) it is clear that the Marcionites were influential enough to have taken up much of his focus.
So why is it that we are so sure that Jesus was a real human being? My difficulties with the idea are very well documented here. It is almost impossible to figure out what this Jesus could have said or done to warrant Jews coercing the Roman rulers of Palestine to crucify him. Claiming to be Christ isn't one of them (and the Marcionites denied that he ever claimed that). The one thing that almost works is that the Jews somehow figured out that his followers knew/thought he was God (John 10:33). An enraged Jewish community might - at least theoretically - have been so enraged that they forced a Roman governors hand.
Of course with regards to the Marcionite gospel, we're dealing with a narrative which claimed that God actually came down from heaven to Judea (Irenaeus Against Heresies 1.27) and then almost everywhere else in Palestine. How 'historical' should we expect that text to be?
There are some very curious features of the narrative which need to be considered. While the canonical texts of Matthew, Mark and John give no specific information about what year or years this 'visitation' took place, Luke is very specific - the fifteenth year of Tiberius Caesar (= 28 CE). That's a very strange feature to have in a fable. Most scholars simply assume that the Marcionite text must have had the same dating, however I think there is good reason to assume that Tertullian's report about the twelfth year of Tiberius (= 25 CE) is reflective of the actual Marcionite text (Against Marcion 1:15).
The reason I find this so interesting is that almost all the other texts agree that Jesus was crucified in the fifteenth year of Tiberius (Acts of Pilate). But know you have a three year interval between the Marcionite dating and Luke which can help explain John - even though Irenaeus's strange interpretation of the chronology in Against Heresies Two throws a wrench into that effort. Perhaps this shows that the text behind John (= the gospel of Justin and Tatian) was already established before Irenaeus.
In any event, it is strange that a narrative about God coming down to earth would be fixed to a certain year. Perhaps the mystical significance of the number twelve (= twelfth disciple, twelfth month, twelfth year) has something to do with it (cf. Irenaeus Against Heresies 2.22) or perhaps there really was an important historical event, well known to contemporary Palestinians but now lost on us, which served as the canvas for this supernatural narrative. We will never likely know for sure.
What is curious is that we find Luke reconstructing a new narrative (Brown Birth of the Messiah p. 251 - 252) around the idea of a twelve year old Jesus entering the Jewish temple. Is it my imagination or is there a wisp of doceticism to the surviving account:
When he was twelve years old (καὶ ὅτε ἐγένετο ἐτῶν δώδεκα), they went up to the festival, according to the custom. After the festival was over, while his parents were returning home, the boy Jesus stayed behind in Jerusalem, but they were unaware of it. Thinking he was in their company, they traveled on for a day. Then they began looking for him among their relatives and friends. When they did not find him, they went back to Jerusalem to look for him. After three days they found him in the temple courts, sitting among the teachers, listening to them and asking them questions. Everyone who heard him was amazed at his understanding and his answers. When his parents saw him, they were astonished. His mother said to him, “Son, why have you treated us like this? Your father and I have been anxiously searching for you.” Why were you searching for me?” he asked. “Didn’t you know I had to be in my Father’s business?" But they did not understand what he was saying to them. Then he went down to Nazareth ... [Luke 1.42 - 51]
It is Ephrem who establishes that the word 'Nazareth' in what follows is referenced as 'Bethsaida' in the Marcionite gospel. We have already demonstrated that 'beth saida' (= house of demons cf. Eccl 2.8 LXX) started out as a reference to the Jewish temple. Now I am starting to wonder whether Jesus's appearance in the temple at 'twelve' is a development of the original order of the Marcionite text.
Already Irenaeus tells us that the Marcosians took interest in this section of text (Against Heresies 1.19.2) I wonder whether the Marcionite gospel just began with:
And in the twelfth year of the reign of Tiberius Caesar ...
dating back to conversations with his grandfather, Gaston Frank. "He said we represent one of the last descendants of the Frankist Jewish faith in the world," he muses. "I grew up thinking that our family was something like the Last of the Mohicans."