47 But, it is said, if the prophets foretold Christ, they did not live in a way becoming their office. How can you tell whether they did or not? You are bad judges of what it is to live well or ill, whose justice consists in giving relief to an inanimate melon by eating it, instead of giving food to the starving beggar. It is enough for the babes in the Catholic Church, who do not yet know the perfect justice of the human soul, and the difference between the justice aimed at and that actually attained, to think of those men according to the wholesome doctrine of the apostles, that the just lives by faith.
"Abraham believed God, and it was counted to him for righteousness. For the scripture, foreseeing that God would justify the Gentiles by faith, preached before the gospel unto Abraham, saying, In your seed shall all nations be blessed." These are the words of the apostle. If you would, at his clear well-known voice, wake up from your unprofitable dreams, you would follow in the footsteps of our father Abraham, and would be blessed, along with all nations, in his seed. For, as the apostle says, "He received the sign of circumcision, a seal of the righteousness of the faith which he had, yet being uncircumcised, that he might be the father of all that believe in uncircumcision; that he might be the father of circumcision not only to those who are of the circumcision, but also to those who follow the footsteps of the faith of our father Abraham in uncircumcision." Since the righteousness of Abraham's faith is thus set forth as an example to us, that we too, being justified by faith, may have peace with God, we ought to understand his manner of life, without finding fault with it; lest, by a premature separation from mother-Church, we prove abortions, instead of being brought forth in due time, when the conception has arrived at completeness.
Source: Reply to Faustus the Manichaean (New Advent)