Galatians 3:7-9

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. 

Understand, then, that those who have faith are children of Abraham 
Luke 3:7-8  John said to the crowds coming out to be baptized by him, "You brood of vipers! Who warned you to flee from the coming wrath? Produce fruit in keeping with repentance. And do not begin to say to yourselves, 'We have Abraham as our father.' For I tell you that out of these stones God can raise up children for Abraham."

"All nations will be blessed through you." 
Genesis 12:3  "I will bless those who bless you, and whoever curses you I will curse; and all peoples on earth will be blessed through you."
Genesis 18:18  "Abraham will surely become a great and powerful nation, and all nations on earth will be blessed through him."
Genesis 22:18  "... and through your offspring all nations on earth will be blessed, because you have obeyed me."
Genesis 26:4-6  "I will make your descendants as numerous as the stars in the sky and will give them all these lands, and through your offspring all nations on earth will be blessed, because Abraham obeyed me and did everything I required of him, keeping my commands, my decrees and my instructions." So Isaac stayed in Gerar.
Acts 3:25  "And you are heirs of the prophets and of the covenant God made with your fathers. He said to Abraham, 'Through your offspring all peoples on earth will be blessed.' "

So those who rely on faith 
Romans 4:16  Therefore, the promise comes by faith, so that it may be by grace and may be guaranteed to all Abraham's offspring--not only to those who are of the law but also to those who have the faith of Abraham. He is the father of us all.

are blessed along with Abraham, the man of faith 
Romans 4:18  Against all hope, Abraham in hope believed and so became the father of many nations, just as it had been said to him, "So shall your offspring be," (Genesis 15:5)

(parentheses are mine)

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