And the Scriptures, foreseeing that God would justify the Gentiles by faith, preached the gospel to Abraham beforehand, saying, “In you all the nations shall be blessed.” (Galatians 3:8)
The gospel is God’s plan to justify the “Gentiles,” the “nations” — the Greek word is the same, ethnoi — to declare them righteous when He comes to judge the world and set things right. It is the good news He preached to Abraham when He promised that He would bless all the nations of the world through him.
The word “justify” means to declare one to be righteous. It is the act of a judge, the decision or finding he makes in a case brought before him. When God justifies you, He finds for you, in your favor, and not against you. It was God’s purpose all along to find for the nations of the earth, and it is happening through Abraham’s seed.
Now to Abraham and his Seed were the promises made. He does not say, “and to your seed,” as of many, but as of one, “And to your Seed,” who is Christ. (Galatians 3:16)This Seed of Abraham is Jesus of Nazareth, descendant of Abraham through Isaac, Jacob, Judah and eventually King David. He is the Messiah who was promised throughout the Old Testament. He was never meant for Israel’s sake alone but as God’s redeeming king for every tribe and tongue on earth.
For you are all sons of God through faith in Christ Jesus. For as many of you as were baptized into Christ have put on Christ. 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. (Galatians 3:26-29)The good news God preached to Abraham, to bless all the nations of the earth through him, is fulfilled in the Seed of Abraham, Jesus the Messiah. Through faith in Him, we too are become Abraham’s seed, both to be blessed and to be a blessing.
(See also The Gospel of the King)