Galatians 3:6-9

Consider Abraham: "He believed God, and it was credited to him as righteousness." Understand, then, that those who believe are children of Abraham.

(v6-7, NIV)

Abraham followed the path of faith. For Abraham, it was through faith that he was justified. Those Jewish Christians probably prided themselves in the fact that they were Jews and descendents of Abraham. However, in their foolishness they didn't even realize that Abraham was justified by faith. If Abraham who they were boasting in was justified by faith, and they were seeking justification by the law, they aren't really following Abraham. Those who live by faith are actually those who are children of Abraham.

The 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 have faith are blessed along with Abraham, the man of faith.

(v8-9, NIV)

God knew before and all along that the Gentiles would be justified by faith. Through the Scripture, which is God-breathed (2 Tim 3:16), we can see that even way back then it was known that the Gentiles would receive justification by faith. Not only do they receive justification, but they are blessed along with Abraham. They share in his blessing. They share in the blessing of the man of faith.