God has promised He will re-join Israel and Judah as one nation again, & restore their fortunes, not because they deserve it, but because He made those promises to Abraham, Isaac, & Jacob. He also promised David that his dynasty would never end nor be interrupted, meaning there would always be a descendant of David's ruling over at least some Israelis somewhere, culminating with Jesus returning to take over David's throne for ever.
These promises are separate from the Church, as they're for Israel only. However, to be saved, each individual Israeli must come to Jesus same as anyone else. There is but ONE plan of salvation for Israeli & gentile alike.