Understand, then, that those who have faith are children of Abraham. Scripture foresaw that God would justify the Gentiles by faith, and announced the gospel in advance to Abraham: “All nations will be blessed through you.” So those who rely on faith are blessed along with Abraham, the man of faith.
Galatians 3:7-9 NIV
In Genesis 13:16, God told Abraham that his descendants would be like the dust of the earth, uncountable. And again, in Genesis 15:5, God told him that his descendants would be as numerous as the stars of the sky. On the surface, it would seem like God’s promise to Abraham had to do just with his physical descendants. And for the following two thousand years, that was the general thought.
But Paul makes it clear here that this promise was not limited to physical descendants. Rather it included all who have faith in the crucified and risen Lord Jesus. It does not matter if you are a Jew or a Gentile. If you have faith in the Lord, then you are a child of Abraham and inherit the promises made to him.
Relationship with God is not a matter of physical descent. Nor is it something that I can earn by my own efforts. It comes to me just like it did with Abraham. He believed and was considered righteous. I believe, and am justified. And I have become a descendant of Abraham in the family of faith.