Actually there is no text in Scripture that literally states that the Jews will turn personally to Jesus of Nazareth as their messiah (that is but an interpretation), however it does explicitly say that God will save the Jews despite their rejection of Jesus. It just doesn’t say that Jews will become Christians in order for God to save them, and mainstream Christian theology teaches that such may not be necessary for Jesus to save even the race that bore him.
Pauline theology is very explicit that the fact that most Jews never turn to Jesus as Messiah does not prevent God from fulfilling his promise to Abraham. In Romans, for instance, Paul never writes that the Jews were loved by God in the past tense, that their disobedience in rejecting Jesus will lead to their current or ultimate rejection. On the contrary, of the Jews he stated: “As regards election, they are beloved, for the sake of their ancestors; for the gifts and the calling of God are irrevocable.” And, “they [the Jews] have now been disobedient [in rejecting Christ] in order that, by the mercy shown you [Christians], they too may now receive mercy. For God has imprisoned all [Christian and Jew and everyone else] in disobedience so that he may be merciful to all [the Christian and the Jew, and everyone else].”--Romans 11.28-32.
The mercy shown now to Christians, Paul writes, is the same that will eventually come to all, Jews too, “for the gifts and calling of God are irrevocable.”
Paul’s message to the Gentile Roman congregation was that despite the current rejection of Jesus as King, God was not abandoning the Jews or incapable of saving them because of their lack of faith, as if God’s love or ability to save was limited by the faithlessness of mere mortals. “Has God rejected his own people? By no means!...God has not rejected his people whom he foreknew.” (Romans 11.1, 2) Paul even claims that Gentiles through Christ are now grafted onto Israel, a meaningless illustration if Israel had been rejected by God. How could being grafted onto a rejected people be of any value? And Israel in this illustration can’t be the new Christian community, as if it replaced Israel somehow, for why would you graft the branches of a tree onto itself if it was already connected to its own roots?
“If the part of the dough offered as first fruits [the Jewish patriarchs] is holy, then the whole batch [including Jews who don’t believe in Christ] is holy,” wrote Paul. He warned as well to the Gentile Christians: “Do not boast over the branches [that have not been gifted with the virtue of faith in Christ]. If you do boast, remember that it is not you [the Gentile Christian] that support the root [brings life to the natural Jews], but the root that supports you.” Christ is the bridge to graft Gentiles into God’s people Israel because Israel is still alive. If Israel is not alive, then you, the wild olive shoot, are actually dead for you have been grafted upon that which has been rejected by God, if indeed God has rejected the Jewish people.--Romans 11.16-24.
Paul concludes by declaring that he does not know by what means God will fulfill his promise to Abraham to save all his children, just that it will be done. (Romans 11.33-36) But one last thing is certain from Paul himself. He was not writing to the Jews in any of his letters, whether they believed in Christ or not.
Acts 21.17-26 shows that Paul paid for a Nazarite vow at the Temple in accordance with the Mosaic Law in order to disprove accusations made against him. According to Acts, the apostles stated that Jewish Christians “are all zealous for the Law.” But some Jewish Christians were troubled since “they have been told that you [Paul] teach all Jews living among the Gentiles to forsake Moses, and that you tell them not to circumcise their children or observe the [Jewish] customs.” Paul made the public act of worship at the Temple in order that “all will know that there is nothing in what they have been told about you, but that you yourself observe and guard the Law.”
The Pauline epistles, as you might already known, are written to Gentile groups, not to Jews. His instruction about not observing the Law, not getting circumcised, not observing Jewish customs according to Acts 21 was never meant to apply to Jews even if they were Christian. Even though he later made a mess of things when he attempted to leave off from eating kosher among Gentiles (Galatians 2.11-14), the apostle Peter, though Christ had already died and risen, himself still followed Jewish dietary laws even well after Pentecost.--Acts 10.9-16.
Also the epistle to the Hebrews (which most scholars attribute to an unknown author), even if it be Pauline, never instructs Jewish Christians to leave off from observing the Law. Neither does it ever say that the Jews have been rejected or that they will eventually turn to Jesus in full faith. In fact, though it tells its readers that Christians have a greater tabernacle than the Jews ever had, it never mentions the Temple, the center of Jewish worship, never even using the word or describing the grand centerpiece of Judaism. Jews never mourned the passing of the tabernacle, but they did the Temple and still do, because it, not the tabernacle of their wanderings, was far greater.
Unfortunately too many Christians have painted in details to make even the New Testament read a certain way that it does not. Instead of being like Paul who could,not say he knew the mystery behind God's way of saving the Jews in Christ, whether this meant a literal turning or not, or even something far beyond what anyone now can imagine, too many make up scenarios and rules that never appear in Scripture about the Jews.
If there is a God, God is not limited by denominational lines, doctrine, or the lack of faith of humans to save.