I will have to get the book. I started a thread awhile back Who is the Vine? Who is the Root? in Bible Questions and Study you may find interesting. I would appreciate your input when you feel more rested. I did a study on it comparing the OT terms applied to Israel and those same terms. "vine" and "root" applied to Jesus in the NT.
Just that one thing puts Dispensationalism's literal thousand years and two peoples in the dust. At least it did for me. One covenant---the Covenant of Redemption with the Godhead, the promise of Gen 3:15, and everything else (including the Old Covenant with the descendants of Jacob and its Law) are a part of, stages of, the plan of the Covenant of Redemption unfolding through history.
@Josheb posted an interesting post there too that brings us back to remembering that it was Jacob whose name was changed to Israel, long before God brought them out of Egypt and into a land.
Israel became a nation made up of the "people of God". Israel inherently encompasses "the people of God" who are in a covenant relationship with him. And that is no longer national/ethnic Israel (they definitely are not as they can no longer have a temple or a High Priest to offer the atonement sacrifice. Plus, in general, they still reject Christ as Messiah). The people of God are those in Christ through faith, in a New Covenant.