[Gen 12:3 ESV] 3 I will bless those who bless you, and him who dishonors you I will curse, and in you all the families of the earth shall be blessed."
Abraham is the father of us all. But Abraham and his descendents only according to the calling of God will bless the earth, one of whom was Christ, who are not naturally born according to the flesh, they must be born according to the Spirit for such persons to bless the world.
Faith is according to Grace, without the grace you could have no faith.
Since our faith is by God's grace, this makes the promise of God sure to all the 'seed' and that seed are not those naturally born.
Romans 4:16-18 New King James Version (NKJV)
16
Therefore it is of faith that it might be according to grace, so that the promise might be sure to all the seed, not only to those who are of the law, but also to those who are of the faith of
Abraham, who is the father of us all 17 (as it is written, “I have made you a father of many nations”) in the presence of Him whom he believed—God, who gives life to the dead and calls those things which do not exist as though they did; 18 who, contrary to hope, in hope believed, so that he became the father of many nations, according to what was spoken, “So shall your descendants be.”
Romans 8
6 But it is not that the word of God has taken no effect. For they are not all Israel who are of Israel, 7 nor are they all children because they are the seed of Abraham; but,
“In Isaac your seed shall be called.” 8 That is, those who are the children of the flesh, these are not the children of God; but
the children of the promise are counted as the seed. 9 For this is the word of promise: “At this time I will come and Sarah shall have a son.”
10 And not only this, but when Rebecca also had conceived by one man, even by our father Isaac 11 (for the children not yet being born, nor having done any good or evil, that the purpose of God according to election might stand, not of works but of Him who calls), 12 it was said to her, “The older shall serve the younger.” 13 As it is written, “Jacob I have loved, but Esau I have hated.”
This is a very important concept to understand.