All of this seems to me to be an instance of creating your own history, a practice not unknown from time to time. A people rises to some prominence, and the rulers and promoters thereof “discover” grand antecedents for themselves. The British did it with their Trojan schtick, the Japanese pretty much invented their whole origins, and so on. And I think, to some extent, Christians did this with their OT antecedents after the break with Judaism.
At this time of year, we read the OT messianic prophecies and we imagine ourselves as ancient Israelites, pining for the coming of the Christ. At other times, as we study the NT in small groups, we frequently cite OT prophecies as if “everyone” knew what they meant and what to expect of them. We have read the Old Testament in light of the New all our lives, and we have exegeted the OT in an “apostolic” manner – perhaps, a “hyper-apostolic” manner, which makes actual Jewish thought on the Tanakh unfamiliar to us. Further, we teach the Jewish features of our religion (which is most of them) to our adherents without ever asking what those look like to the Jews among us. Christian Jewishness sometimes doesn’t bear a lot of resemblance to Jewish Jewishness, I’m afraid.
Now, to be fair, when two groups find themselves tangled up with each other, they tend to define themselves over against each other. It’s not just that they start looking for differences, but they start magnifying differences where they can. In the case of Christianity emerging from Judaism in the First Century, once the first wave of evangelism was over, the Jews who had rejected Jesus’ messiahship found themselves in a polemical war over their Jewish heritage. They began de-emphasizing some things that had been rather common, such as the doctrine of the resurrection. Christians, meanwhile, began to assert ownership of ideas that they had inherited from Judaism.
Note: both groups were being pretty honest. No one really consciously invented anything, certainly not out of whole cloth. But over time, each came up with a different take on their common origin. The Jews, of course, maintained primary ownership of their own legacy because they remained Jews. The Christians, who had to cede Jewishness to the Jews, necessarily evolved a different explanation of things. Just a matter of point of view, really.
When this sort of tendency is combined with the fundamentalist/evangelical view of Scripture, then things get really strange. For evangelicals, “the Bible” is a self-authenticating text, a book inspired by God almost to the point of spirit-writing. Their view of Scripture approaches the idea “that God so loved the world that he gave” us an infallible rule book. Which might be almost defensible if they were defending the Scriptures the apostles knew. but the elision of the deuterocanonical books following the polemical war between early Protestants and Counter-Reformation Catholics poses an interesting question of authenticity. Just as Christians made their own history out of the common heritage they shared with Jews (and so did the Jews), so Protestants made their own sources of authority out of the tradition they shared with Catholics (and so did the Catholics).
Please note that I’m not questioning the authenticity of the Scriptures themselves, nor their authority for Christians as the last appeal on matters of moment within the Church. I believe the Bible, even if I am careful about the idea of “believing in” the Bible. Which means I find myself constantly caught between butter-wouldn’t-melt-in-their-mouths progressives who show little regard for the integrity of the Scriptures and aggressive evangelicals who insist on the integrity of the Bible, without admitting that they have carefully edited that Bible and surrounded it with a tradition that insists that Tradition is subordinate to the Scriptures themselves.
Honesty would seem to require us to admit what we have done at each stage of the development of our tradition. Maybe how we got to where we are is entirely legitimate, but then we shouldn’t be shy about ‘fessing up to our part in it.