John Chrysostom
“As it is written: ‘I have made you the father of many nations.’” Do you see that this was established from ancient times? But what then? You will object: perhaps this is said of the Ishmaelites, Amalekites, or Hagarenes?
Later the Apostle proves more clearly that it was not said of them. For the moment, to confirm the same point, he hastens to another argument, defining the manner of this kinship and unfolding it with great depth.
What does he say? “Before God, in Whom he believed.” The meaning of these words is this: as God is not a partial God, but Father of all, so also is Abraham.
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And again: as God is our Father not by natural kinship, but by the adoption of faith, so also is Abraham. For obedience makes him father of us all. Since the Jews thought such kinship had no significance after they had received another, coarser kinship, the Apostle transfers the argument to God and proves that kinship by faith is far more important.
At the same time, he reveals that Abraham received this as a reward for faith. If this were not so, then even if he were father of all living on earth, the expression “before God” would have no place. The gift of God would be diminished. The word “before” means “like.”
Tell me, indeed, what is marvelous about being father of those who descend from him? This is common to every man. But the marvelous thing is that, by God’s gift, he received as children those who were not his by nature. Therefore, if you wish to believe that the patriarch was counted worthy of honor, believe that he is father of all.
After saying, “before God, in Whom he believed,” the Apostle did not stop there, but added: “Who gives life to the dead and calls the things that do not exist as though they existed.” Here he introduces a preliminary discourse on the resurrection, which he needed for the present subject.
If it is possible for God to give life to the dead and bring into being what does not exist, then it is also possible for Him to make those not born from Abraham into his children. Therefore the Apostle did not say, “bringing into being what does not exist,” but “calling,” indicating the great ease of this work for God.
As it is easy for us to name what exists, so it is easy for Him, and far easier, to bring into being what does not exist. And when the Apostle says that God’s gift is great and ineffable, and when he speaks of its power, he proves that Abraham’s faith was worthy of this gift, so that you should not think Abraham was honored without merit.
Thus, having encouraged the hearer not to be troubled, and so that the Jew might not object and say, “How can those who are not children be made children?” the Apostle again turns the discourse to the patriarch and continues: Rom 4:18. “Who, against hope, believed in hope, that he might become the father of many nations, according to what was spoken: ‘So shall your seed be.’”