7 nor are they all children because they are the seed of Abraham; but, “In Isaac [not Ishmael] your seed shall be called.”
In verses seven through nine we have the case of Isaac and Ishmael, two sons of Abraham. The premise of these verses rests on the foundation of the nation of Israel by regeneration, not by physical birth. Isaac was regenerated but not Ishmael. Isaac was the father of Jacob and Esau. Jacob was regenerate but not Esau.
Isaac and Jacob were truly regenerate but not Ishmael and Esau. Not all Israelites are descendants of Isaac and Jacob, which is the point of this section. Neither can all the descendants of Jacob presume on their physical lineage (Ro 9:10-13). The point here is that there is a true regenerate Israel that goes beyond natural lineage.
The idea that spiritual Israel includes Gentiles is never taught in Scripture. Throughout Romans chapters 9 to 11, God makes a distinction between the Gentiles and Israel.
In verses 14 to 18, there is a third illustration about Pharaoh, showing that God’s way of salvation is His prerogative.
but [strong contrast], “In Isaac your seed shall be called [derive their name from Isaac].”
Abraham had two sons: Isaac and Ishmael. Although Ishmael was Abraham’s physical seed, God chose to work through Isaac. Isaac was regenerate but Ishmael was not.
The phrase “In Isaac your seed shall be called” is a quotation from Genesis 21:12 whereby God told Abraham that his seed would come through a regenerate line by promise.
Gal 3:29, And if you are Christ’s, then you are Abraham’s seed, and heirs according to the promise.
Physical descendants are not “called.” But by strong contrast Genesis 21 proves that only those of the promise, such as Isaac, are saved. Isaac was a child of the promise, not Ishmael. Regeneration determines who is a true Israelite. That is why God’s promise did not fail (v. 6). God’s promise to Abraham would never be realized to each ethnic Israelite but only to those who would believe.
Ro 2:28-29, 28 For he is not a Jew who is one outwardly, nor is circumcision that which is outward in the flesh; 29 but he is a Jew who is one inwardly; and circumcision is that of the heart, in the Spirit, not in the letter; whose praise is not from men but from God.
God’s call always goes out to those who accept the promise. He never fails in this. He is always just in His way of salvation.
God is free to choose Isaac and reject Ishmael. The calling here is in the context of national as well as personal calling. However, corporate election cannot justify individuals in the nation. This calling here, therefore, has to do with personal faith in the Messiah or Christ and the calling of the theocratic nation Israel. It is God’s unilateral establishment of a nation by promise that is a guarantee.
Ga 3:6-7, 6 just as Abraham “believed God, and it was accounted to him for righteousness.” 7 Therefore know that only those who are of faith are sons of Abraham.
This section of Romans chapter nine deals with the foundation of a unique nation. Abram was a Gentile who became the first Jew. Having believed God’s covenant toward him (the Abrahamic covenant, Ge 12-15), he became regenerate. God began a new nation based on regeneration.
Abraham had two sons by different mothers, one was regenerate (Isaac) and the other not (Ishmael). They both had the same father but not the same spirituality. The first birth is not the issue with God; it is the second birth. Isaac was born again, truly regenerated. The argument of Romans is the righteousness of God; God is righteous by declaring righteous those who believe His promise. In other words, justification relates to the theodicy of this chapter.
Isaac had twins: Esau and Jacob (the younger). Esau was a lost but Jacob was saved. The foundation of the Jewish people is regeneration, not natural generation. Why is Isaac the key in this verse? He was born again—regenerated.
God is just in His ways.
The reason people in the Old Testament were saved by the principle of justification is that God must deal with Himself. He is perfect righteousness and He must deal justly with Himself. If He compromised His own character, He would not be just. That is why Abraham believed God and it was calculated to him for righteousness (Ge 3:15). Part of the defense of the character of God is the just way He deals with Himself and others.