The Israel of God is the body of Christ...the
spiritual descendants of Abraham. Not the physical descendants of Abraham.
Galatians 3:16
Now the promises were made to Abraham and to his offspring. It does not say, “And to offsprings,” referring to many, but referring to one, “And to your offspring,” who is Christ.

Galatians 3:29
And if you are Christ’s, then you are Abraham’s seed, and heirs according to the promise.
Romans 9:6-8
It is not as though God’s word had failed. For not all who are descended from Israel are Israel. 7 Nor because they are his descendants are they all Abraham’s children. On the contrary, “It is through Isaac that your offspring will be reckoned.” 8 In other words, it is not the children by physical descent who are God’s children, but it is the children of the promise who are regarded as Abraham’s offspring.
Romans 2:28-29
For he is not a Jew who is one outwardly, nor is circumcision that which is outward in the flesh; 29 but he is a Jew who is one inwardly; and circumcision is that of the heart, in the Spirit, not in the letter; whose praise is not from men but from God.
Galatians 3:28-29
"There is neither Jew nor Greek, there is neither slave nor free, there is neither male nor female; for you are all one in Christ Jesus. And if you are Christ’s, then you are Abraham’s seed, and heirs according to the promise."