How can the Gentiles be included in the promises made to Israel? Does this not do damage to the Old Testament? What about those promises given to Abraham?
What we see in both old and new testaments is that Christ is the fulfillment of Israel and the one whom is the rightful heir of all the promises of God. It is through Christ that the Gentiles and Jews receive their inheritance and blessing. Christ is the key, the cornerstone, the center of God's plan, and the one to whom all of Scripture points.
See Christ high and exalted!