Galatians 3:6

Moreover, do not be unbelieving toward the forefather Abraham, for he too was justified by faith.

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.

(Verse 6.) Just as Abraham believed God, and it was counted to him as righteousness. From this place until where it is written: Those who are of faith are blessed with faithful Abraham, Marcion erased from his Apostle. But what profit was there in embracing this, when the other things he left behind, his insanities, are opposed to it? Yet Abraham believed God, going out from his country into a land he did not know (Gen. 12 ff.): trusting that Sarah, who was ninety years old and barren, would give birth; and hearing the promise of God that his offspring would be called through Isaac, he offered Isaac as a sacrifice, and yet did not doubt the promise of the Lord. The faith is rightly considered to contribute to justice, the one who, having gone beyond the works of the Law, has deserved God not out of fear, but out of love.

Also in the priest Melchizedek we see prefigured the sacrament of the sacrifice of the Lord, according to what divine Scripture testifies, and says, "And Melchizedek, king of Salem, brought forth bread and wine." Now he was a priest of the most high God, and blessed Abraham. And that Melchizedek bore a type of Christ, the Holy Spirit declares in the Psalms, saying from the person of the Father to the Son: "Before the morning star I begat Thee; Thou art a priest for ever, after the order of Melchizedek; " which order is assuredly this coming from that sacrifice and thence descending; that Melchizedek was a priest of the most high God; that he offered wine and bread; that he blessed Abraham. For who is more a priest of the most high God than our Lord Jesus Christ, who offered a sacrifice to God the Father, and offered that very same thing which Melchizedek had offered, that is, bread and wine, to wit, His body and blood? And with respect to Abraham, that blessing going before belonged to our people. For if Abraham believed in God, and it was accounted unto him for righteousness, assuredly whosoever believes in God and lives in faith is found righteous, and already is blessed in faithful Abraham, and is set forth as justified; as the blessed Apostle Paul proves, when he says, "Abraham believed God, and it was accounted to him for righteousness. Ye know, then, that they which are of faith, these are the children of Abraham. […]

Even the miracles done by themselves, he says, declare the power of Faith, but I shall attempt if you will suffer me to draw my proofs from ancient narratives also. Then, as they made great account of the Patriarch, he brings his example forward, and shows that he too was justified by Faith. And if he who was before grace, was justified by Faith, although plentiful in works, much more we. For what loss was it to him, not being under the Law? None, for his faith sufficed unto righteousness. The Law did not then exist, he says, neither does it now exist, any more than then. In disproving the need of the Law, he introduces one who was justified before the Law, lest an objection should also be made to him; for as then it was not yet given, so now, having been given, it was abrogated. And as they made much of their descent from Abraham, and feared lest, abandoning the Law, they should be considered strangers to his kin; Paul removes this fear by turning their argument against themselves, and proves that faith is especially concerned in connecting them with Abraham. He draws out this argument more at length in the Epistle to the Romans; however he urges it also here in, the words...