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.
8 That is,
Paul now gave his thrust of what the quote of Genesis 21:12 means. He clarified that “children” means regeneration. He was about to give the basis for choosing Isaac, about how a regenerate nation began.
those who are the children of the flesh [physical children; ethnic Jews], these are not the children [born ones, or regenerate ones; regenerate Jews] of God;
It is not physical Israel who are truly regenerate but those who personally accept the Abrahamic covenant by faith (Ge 15:6). There is a difference between physical children and spiritually regenerate children. Natural descent and spiritual rebirth are two different things. There are children who are born of God, regenerate. The latter is a filial relationship with God, not a physical relationship (4:13-21).
but [strong contrast] the children [regenerate ones] of the promise are counted [calculated] as the seed.
True Israelites are those who believe the “promise.” God counts or calculates them as His true “seed.” We saw this word “counted” or calculated in chapter four:
Ro 4:3, For what does the Scripture say? “Abraham believed God, and it was accounted to him for righteousness.”
Ro 4:22-24, 22 And therefore “it was accounted to him for righteousness.” 23 Now it was not written for his sake alone that it was imputed to him, 24 but also for us. It shall be imputed to us who believe in Him who raised up Jesus our Lord from the dead,
Salvation is only through God’s reckoning.
God’s children are God’s children by reckoning, not by works. This is an issue of God’s justice. God’s people are the children of promise; spiritual birth is not due to anything in ourselves, but rather it rests entirely on God’s promise. It is promise that gives spiritual birth.
Jn 1:11-13, 11 He came to His own [things, neuter], and His own [people, masculine] did not receive Him. 12 But as many as received Him, to them He gave the right to become children of God, to those who believe in His name: 13 who were born, not of blood, nor of the will of the flesh, nor of the will of man, but of God.
Our “right” has to do with God’s righteousness. God is just in all that He does.
Ge 18:25, “Shall not the Judge of all the earth do right?”
On a human level it is not possible to protect the rights of people without destroying society. This is not to say that there is no need for law; law is needed to protect society, not to make society anew. We cannot make people like each other. Some white people do not accept other white people; there are African Americans who do not accept those of their own ethnic race either. We find justice only in God and His Word.