Does Jeremiah's “New Covenant” abrogate the “Davidic Covenant?”
Pathways:
Whatever your issue over Christanity vs. Judaism, there is a fundamental question that needs to be asked; are these covenants complimentary or exclusionary? If they are complimentary. how is it possible that David and Solomon were justified without the salvation of Jesus, and if it is exclusionary, I.E. if it changes the thing, why did God state that it was an eternal covenant? If God's prophecies do not come true from the Old Testament, that could be a major problem – However, if God's prophecies from the New Testament come true, that would likely be the only way of verifying which one was correct, barring a full exposition from the text (see covenant studies above).
I'd propose the purpose of the text is to provide sufficient exposition for a true believer to make a decision – i.e. the “living religion” argument from above that lets us go from first mover to abrahamic God. Therefore, we have to be able to discern from a scriptural study of these covenants which denomination is correct – it is not possible that we can only understand the text in retrospect, because in that case the text itself would not be necessary.