Some popular Christian beliefs about salvation started among Diaspora Jews, inspired by Roman and Greek mythology, which they read into Jewish scriptures. For example, a celestial being similar to an archangel, buying salvation for us by suffering, dying and being raised again.
An interesting hypothesis, one that is being explored by modern scholarship, without reverting to total and rather extreme position of the mythicists.
A particular problem you'd have to overcome is that the idea of buying salvation by suffering, dying and being raised again is, I think, absent from GrecoRoman mythology. In their view, heroes and demigods die and go to heaven; some die at the hands of others, such as Hercules, and possibly the wonder-worker Apollonius of Tyana, but none died for the the sake of others, for the salvation of many, or the overcoming of sin.
For the Jews, the influence of Hellenic myth might have had some influence on the idea that Enoch was understood to have been assumed into heaven, as a divinised and/or ‘angelised’ mortal, as was Elijah after him. But again, like their GrecoRoman counterparts, these divine elevations were regarded as the just rewards of their own righteousness, rather than any idea of sacrifice on behalf of many ...
When the Jerusalem apostles found them, they interpreted those beliefs as being inspired by visions of their own Kyrios Yeshua Chrestos. How could they think otherwise?
Having said all the above, there is scope to admit and accept that popular mythological tropes were grafted onto the person of Jesus, but not the central principle of a sacrificial death and resurrection – for Paul, the Resurrection underpins the totality of the gospel, without that single element, the rest becomes meaningless – St Paul said it most emphatically –
"But if Christ is proclaimed – that he has been raised from the dead – how is it some among you say that there is no resurrection of the dead? Now, if there is no resurrection of the dead, then neither has Christ been raised; and if Christ has not been raised then our proclamation is vain, and your faith vain; and also we are found to be false witnesses of God, because we testified of God that he raised Christ, whom he did not raise if the dead are not raised; for, if the dead are not raised, then Christ has not been raised either; and if Christ has not been raised your faith is futile: you are still in your sins." (1 Corinthians 15:12-17).
For Paul, and for the early Christian kerygma, this is the one inarguable, fundamental point, Christ died, for the sake of all, and was raised from the dead. If you don't believe that, Paul argues, then the whole enterprise is pointless.
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The writings around Christianity – Paul, the Gospels, and so forth, were penned by Jews who were the product of a world by then thoroughly Hellenised. The question then is, to what degree? The Jews at Qumran and the Jews living in Alexandria had very different relationships with the wider Hellenic culture, but it's probably more the case that the Alexandrians were more conscious of their Hellenisation than the Essenes. Scholars of Early Christianity now see the Jesus Movement of the first century as fully within the cultic, social and institutional boundaries of what we would identify as 'Judaism,' but a Judaism that arose within a GrecoRoman mileau.
The authors of the New Testament were primarily Jews within the broad matrix of Early Jewish diversity and the cultural mix of Hellenism.
And there has also been a very great deal of illuminating scholarship in recent years on the consonance between early Christian literature, the Gospels in particular, and the literature of late antique pagan culture (David C Miller and Robyn Faith Walsh have made contributions in this field).
D.B Hart would argue that had Christianity died out; if we found, say, the Gospels in a cache in some cave somewhere, they would not strike scholars as noticeably unusual or out of place in the classical canon of their era. They would be taken as an example of the same kind of work as Philostratus’s
Life of Apollonius – yet another wonderworker, another sage uttering impenetrable oracles, another mysterious itinerant holy man harbouring secrets he could divulge only to his inner circle, just another 'divine mortal' unfairly arraigned before human judges.
Does that render the Gospels as myth?
No. That idea passed with that giant of Christian theological speculation, Rudolf Bultmann:
A is a myth, B reads like A, therefore B is a myth ... a flawed thesis which proved remarkably popular, for a while, then evaporated.
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The problem to be addressed here is that the mystery of Christ is unintelligible if it is wholly dissimilar to everything else culturally.
If Christ has no parallel in world mythology, philosophy, and religion, then all one has done is make a Jesus utterly inaccessible to one's audience, indeed to any meaningful conceptualisation.
So the literary forms of the Gospels reflect the literary conventions and idioms of their time. How could they not? They incorporate motifs and tropes and episodes that were part of the common grammar of a kind of literature that aspired
not to historical accuracy (as we now reckon such things), but rather to illustrate those deeper truths about its subject. It's not that the authors did reflect those conventions, it's simply a fact that
they had to, had they not, then their testimonies would have been inaccessible.
What we cannot do, although we often try, is to fit the narratives into a convenient genre of our own sensibility – Gospels are not 'history', but that does not mean they are fiction, that's to commit an anachronism and an injustice.
It's not so much two Jesus', as one Jesus who is required in certain respects to 'tick the boxes' of Judeo-Greco-Roman spiritual and metaphysical speculation.
