Ezekiel 37 does talk about reuniting the northern and southern kingdoms, but here’s the part you’re missing: Ezekiel gives the vision in Israel’s own categories, but the New Testament tells you what those categories ultimately point to. The prophets always speak in the symbolic world of Israel’s history — tribes, land, kings, temple, exile — because that’s the language their audience understands.
But the apostles consistently show that those symbols reach their final fulfillment in Christ’s kingdom, not in a rebuilt geopolitical Israel. So you’re right that Ezekiel 37 depicts the reunification of the twelve tribes; what you’re not seeing is how Scripture says that reunification actually happens.
Ezekiel 37’s two sticks represent the historic division between Judah and Israel, but the NT says the true reunification happens when Christ creates one new people out of Jew and Gentile (Ephesians 2), which is why Paul calls the Church “the Israel of God” (Galatians 6:16) and why James addresses the twelve tribes in diaspora as believers in Christ (James 1:1); the prophets use Israel’s tribal imagery to describe the restoration of God’s people, but the apostles reveal the mystery that the restored people are those united to the Messiah, not a future political merger of ancient tribes; this is exactly how prophetic fulfillment works — Isaiah’s Zion becomes the worldwide people of God, Jeremiah’s New Covenant becomes the covenant in Christ’s blood, Amos’s rebuilt Davidic tent becomes the Gentile inclusion (Acts 15), and Ezekiel’s reunited tribes become the one body of Christ; you’re treating Ezekiel’s imagery as the final form, but Scripture itself shows that prophetic symbols expand into their Christ‑centered fulfillment, meaning the “whole house of Israel” is not a future tribal census but the unified people of God brought together under the one Shepherd, the Son of David
I guess I've always viewed this a little bit differently. I've always believed that "all Israel will be saved" included believing Jews, Gentiles, and the land of Israel itself for the purpose of the Millennial Kingdom period before the New Jerusalem made our relationship together as permanent and different.
I still sincerely believe that the whole purpose of the Millennial Kingdom period was for Jesus to fulfill the Abrahamic & Davidic covenants for the people that He has always claimed that He "has set apart" before we're all joined together in the New Jerusalem, so that the number of cultural Jews would significantly increase before the permanent kingdom sets in. While I know there will be no difference between Jews & Gentiles in the permanent kingdom, I believe the Millennial Kingdom has been set apart for this reason. A fulfilled promise literally, physically, and spiritually.