Cool. Here's a starting point:

Galatians 3:7-9

> [7] Know then that it is those of faith who are the sons of Abraham. [8] And the Scripture, foreseeing that God would justify the Gentiles by faith, preached the gospel beforehand to Abraham, saying, “In you shall all the nations be blessed.” [9] So then, those who are of faith are blessed along with Abraham, the man of faith.

Or Romans 2:26-29

> [26] So, if a man who is uncircumcised keeps the precepts of the law, will not his uncircumcision be regarded as circumcision? [27] Then he who is physically uncircumcised but keeps the law will condemn you who have the written code and circumcision but break the law. [28] For no one is a Jew who is merely one outwardly, nor is circumcision outward and physical. [29] But a Jew is one inwardly, and circumcision is a matter of the heart, by the Spirit, not by the letter. His praise is not from man but from God.

Or Romans 9:6-8

[6] But it is not as though the word of God has failed. For not all who are descended from Israel belong to Israel, [7] and not all are children of Abraham because they are his offspring, but “Through Isaac shall your offspring be named.” [8] This means that it is not the children of the flesh who are the children of God, but the children of the promise are counted as offspring.

Or the entire chapter of Romans 11.

That should serve as a good start for consideration.

God's covenant with Abraham continues, not through physical descentants of Abraham, but through those who share the same faith that Abraham had and it was counted to him for righteousness.

Ah, that reminds me... Should have included all of Romans 4.