The promises are hinged on you fulfilling the law, which Israel, obviously, has not. A Jew is one inwardly, not according to the flesh, but in the spirit, by the circumcision made without hands:
1Sa_16:7; 1Ch_29:17; Psa_45:13; Jer_4:14; Deu_10:16, Deu_30:6; Jer_4:4.
Christians have the better claim to the name of Israel. Christ fulfilled the law, you have not and cannot, and we are joined to the church through Him.
G-d’s promises were made (for the most part, and specifically the one I referenced in Genesis 12:3) to Abraham, Isaac and/or Jacob BASED ON THEIR ACTIONS DURING THEIR LIVES, and were clearly intended to be forever, to inure to ALL of their descendants. Since it was G-d making those promises, and He does not lie like humans, and he knows the future perfectly, it is not only a covenant forever, but it is both logically and theologically ABSURD that He would withdraw His promises. That simply CAN’T happen.