Gal 3:7

“For ye are all the children of faith," it becomes dear that what the heretic's industry erased was the mention of Abraham's name; for by faith the apostle declares us to be "children of Abraham," and after mentioning him he expressly called us "children of faith" also. But how are we children of faith? and of whose faith, if not Abraham's? For since "Abraham believed God, and it was accounted to him for righteousness; " since, also, he deserved for that reason to be called "the father of many nations," whilst we, who are even more like him in believing in God, are thereby justified as Abraham was, and thereby also obtain life-since the just lives by his faith,-it therefore happens that, as he in the previous passage called us "sons of Abraham," since he is in faith our (common) father, so here also he named us "children of faith," for it was owing to his faith that it was promised that Abraham should be the father of (many) nations.”

“For if "faith" is the source whence we are reckoned to Abraham as his "sons" (as the apostle teaches, saying to the Galatians, "You know, consequently, that (they) who are of faith, these are sons of Abraham"), when did Abraham "believe God and it was accounted to him for righteousness?" I suppose when still in monogamy, since (he was) not yet in circumcision. But if afterwards he changed to either (opposite)—to digamy through cohabitation with his handmaid, and to circumcision through the seal of the testament—you cannot acknowledge him as your father except at that time when he "believed God," if it is true that it is according to faith that you are his son, not according to flesh. ... In like manner, too, if you have involved yourself in digamy, you are not the son of that Abraham whose "faith" preceded in monogamy. For albeit it is subsequently that he is called "a father of many nations," still it is of those (nations) who, as the fruit of the "faith" which precedes digamy, had to be accounted "sons of Abraham."”

“Every mystery which is enacted by our Lord Jesus Christ asks only for faith. The mystery was enacted at that time for our sake and aimed at our resurrection and liberation, should we have faith in the mystery of Christ and in Christ. For the patriarchs prefigured and foretold that man would be justified from faith. Therefore, just as it was reckoned as righteousness to Abraham that he had faith, so we too, if we have faith in Christ and every mystery of his, will be sons of Abraham. Our whole life will be accounted as righteous.”

“(V.7) So you know, those who are of faith, these are the children of Abraham. He discusses more fully in the letter to the Romans that faith was reckoned to Abraham as righteousness, not in circumcision but in uncircumcision (Rom. 4). And carefully observing, he teaches that those who believed with this mindset are the children of Abraham, just as Abraham believed when he was uncircumcised, who rejoiced to see the day of the Lord, and saw it and was glad (John 8). And it is also said to the unbelieving Jews: If you were children of Abraham, you would do the works of Abraham (Ibid. 39). But what other works was the Lord seeking from them at that time when these things were said, except faith in the Son of God, whom the Father had sent to speak: Whoever believes in me, does not believe in me, but in him who sent me (John XII, 44)? And in another place, when they were clapping and boasting about their ancient and noble lineage, the response is given: And do not say, 'We have Abraham as our father.' For God is able to raise up children to Abraham from these stones (Matth. III, 9). By these stones, no one doubts that the hardened hearts of the Gentiles are signified, which were later softened and received the seal of faith. Enumerate the virtues of Abraham in which he pleased God before circumcision, diligent reader, and wherever you find them in a similar work, say that they are the children of Abraham, justified in the foreskin, who received circumcision not because of the merit of works, but as a sign of prior faith. For indeed Christ was to be born from his seed (in whom the blessing of all nations was promised, and from Abraham until Christ many centuries were to pass), God foreseen that the children of beloved Abraham might mix with other nations, and gradually his family would become uncertain, he marked the Israelite flock with a certain circumcision seal, so that they would be distinguished by this sign while living among the Egyptians, Assyrians, Babylonians, and Chaldeans. Finally, for forty years in the desert, no one was circumcised: for they alone lived without the mixture of another nation. As soon as the people crossed the banks of the Jordan and poured themselves into the land of Palestine, the circumcision, necessary for the future mix of nations, guarded against error. And that which is written a second time about the circumcised people (Joshua 5) signifies that the circumcision ceased in the desert, which was reasonably practiced in Egypt; and that believers are to be cleansed by the spiritual circumcision of the Lord Jesus Christ.”

“From this authority he draws the minor proposition, saying "Know ye therefore, that they who are of faith, the same are the children of Abraham." As if to say: Someone is called the son of another because he imitates his works; therefore, "if you be the children of Abraham, do the works of Abraham" (Jn 8:39). But Abraham did not seek to be justified through circumcision but through faith. Therefore the sons of Abraham are they who seek to be justified by faith. And this is what he says: Because Abraham is just through faith, in that he believed God and it was reputed to him unto justice; "therefore, know ye that they" who are of faith, i.e., who believe that they are justified and saved by faith, "the same are the children of Abraham," namely, by imitation and instruction: "They that are the children of the promise are accounted for the seed" (Rom 9:8); "This day is salvation come to this house, because he also is the son of Abraham" (Lk 19:9); "God is able of these stones," i.e., of the Gentiles, "to raise up children to Abraham," inasmuch as He makes them believers (Mt 3:9).”

“Since they were afraid to abandon the law, for fear that they fall away from the kinship of Abraham, he turns the argument the other way. The "then," [ἄρα] is "so therefore" [τοιγαροῦν]. "that those who are of faith." Therefore these were especially opposed to the law, scorning its antiquity. It must then be shown that faith was established before the law, and that above all by it one is pleasing to God from above.”