2 For if Abraham were justified by works, he hath whereof to glory; but not before God.
[AD 407] John Chrysostom on Romans 4:1-2
"What shall we then say that Abraham, our father as pertaining to the flesh, has found? For if Abraham were justified by works, he has whereof to glory; but not before God."

He had said (5 manuscripts εἶπεν]), that the world had become guilty before God, and that all had sinned, and that boasting was excluded and that it was impossible to be saved otherwise than by faith. He is now intent upon showing that this salvation, so far from being matter of shame, was even the cause of a bright glory, and a greater than that through works. For since the being saved, yet with shame, had somewhat of dejection in it, he next takes away this suspicion too. And indeed he has hinted at the same already, by calling it not barely salvation, but "righteousness. Therein" (he says) "is the righteousness of God revealed." [Romans 1:17] For he that is saved as a righteous man has a confidence accompanying his salvation. And he calls it not "righteousness" only, but also the setting forth of the righteousness of God. But God is set forth in things which are glorious and shining, and great. However, he nevertheless draws support for this from what he is at present upon, and carries his discourse forward by the method of question. And this he is always in the habit of doing both for clearness sake, and for the sake of confidence in what is said. Above, for instance, he did it, where he says, "What advantage then has the Jew?" [Romans 3:1] and, "What then have we more than they?" [Romans 3:9] and again, "where then is boasting? It is excluded" [Romans 3:27]: and here, "what then shall we say that Abraham our father?" etc. Now since the Jews kept turning over and over the fact, that the Patriarch, and friend of God, was the first to receive circumcision, he wishes to show, that it was by faith that he too was justified. And this was quite a vantage ground to insist upon (περιουσία νίκης πολλἥς). For for a person who had no works, to be justified by faith, was nothing unlikely. But for a person richly adorned with good deeds, not to be made just from hence, but from faith, this is the thing to cause wonder, and to set the power of faith in a strong light. And this is why he passes by all the others, and leads his discourse back to this man. And he calls him "father, as pertaining to the flesh," to throw them out of the genuine relationship (συγγενείας γνησίας) to him, and to pave the Gentiles' way to kinsmanship with him. And then he says, "For if Abraham were justified by works, he has whereof to glory: but not before God." After saying that God "justified the circumcision by faith and the uncircumcision through faith," and making the same sufficiently sure in what he said before, he now proves it by Abraham more clearly than he promised, and pitches the battle for faith against works, and makes this righteous man the subject of the whole struggle; and that not without special meaning. Wherefore also he sets him up very high by calling him "forefather," and putting a constraint upon them to comply with him in all points. For, Tell me not, he would say, about the Jews, nor bring this man or that before me. For I will go up to the very head of all, and the source whence circumcision took its rise. For "if Abraham," he says, "was justified by works, he has whereof to glory: but not before God." What is here said is not plain, and so one must make it plainer. For there are two "gloryings," one of works, and one of faith. After saying then, "if he was justified by works, he has whereof to glory; but not before God;" he points out that he might have whereof to glory from faith also, yea and much greater reason for it. For the great power of Paul is especially displayed in this, that he turns what is objected to the other side, and shows that what seemed rather to be on the side of salvation by works, viz. glorying or boldness of claim (παρρησιάζεσθαι) belonged much more truly to that by faith. For he that glories in his works has his own labors to put forward: but he that finds his honor in having faith in God, has a much greater ground for glorying to show, in that it is God that he glorifies and magnifies. For those things which the nature of the visible world tells him not of, in receiving these by faith in Him, he at once displays sincere love towards Him, and heralds His power clearly forth. Now this is the character of the noblest soul, and the philosophic spirit, and lofty mind. For to abstain from stealing and murdering is trifling sort of acquirement, but to believe that it is possible for God to do things impossible requires a soul of no mean stature, and earnestly affected towards Him; for this is a sign of sincere love. For he indeed honors God, who fulfils the commandments, but he does so in a much greater degree who thus follows wisdom (φιλοσοφὥν) by his faith. The former obeys Him, but the latter receives that opinion of Him which is fitting, and glorifies Him, and feels wonder at Him more than that evinced by works. For that glorying pertains to him that does aright, but this glorifies God, and lies wholly in Him. For he glories at conceiving great things concerning Him, which redound to His glory. And this is why he speaks of having whereof to glory before God. And not for this only, but also for another reason: for he who is a believer glories again, not only because he loves God in sincerity, but also because he has enjoyed great honor and love from him. For as he shows his love to Him by having great thoughts about Him, (for this is a proof of love), so does God also love him, though deserving to suffer for countless sins, not in freeing him from punishment only, but even by making him righteous. He then has whereof to glory, as having been counted worthy of mighty love.

[AD 253] Origen of Alexandria on Romans 4:2
This is a rhetorical argument, which goes like this: Someone who is justified by works has nothing to boast of before God. But Abraham did have something to glory in before God. Therefore he was justified by faith and not by works.In this whole passage it seems that the apostle wants to show that there are two justifications, one by works and the other by faith. He says that justification by works has its glory but only in and of itself, not before God. Justification by faith, on the other hand, has glory before God, who sees our hearts and knows those who believe in secret and those who do not believe. Thus it is right to say that it has glory only before God, who sees the hidden power of faith. But the one who looks for justification by works may expect honor mainly from other persons who see and approve of them.
Let no one think that someone who has faith enough to be justified and to have glory before God can at the same time have unrighteousness dwelling in him as well. For faith cannot coexist with unbelief, nor can righteousness with wickedness, just as light and darkness cannot live together.

[AD 384] Ambrosiaster on Romans 4:2
This is a rhetorical argument. For Abraham indeed does have glory before God, but because of the faith by which he was justified, because nobody is justified by the works of the law in a way which would give him glory before God. And because those who keep the law are still being justified, Paul adds: “If Abraham was justified by works, he has something to boast about, but not before God.”

[AD 407] John Chrysostom on Romans 4:2
For someone to be justified by faith if he had no works was unusual. But for one who had plenty of good works to delight in being justified not by works but by faith—that was something to cause amazement. It put the power of faith in a new light.What Paul is saying here is not plain, and so it is necessary to make it clearer. There are two kinds of boasting—one of works and one of faith.… Paul’s great strength is particularly displayed in this, that he turns the objection around and shows that what seemed to favor the idea of salvation by works (viz., boasting) belonged much more truly to salvation by faith. For the man who boasts in his works is boasting about himself, but the man who finds his honor in having faith in God has a much better reason for boasting, because he is boasting about God, not about himself. … To abstain from stealing or murder is a minor accomplishment compared to believing that God can do the impossible.… The believer boasts not only because he sincerely loves God but also because he has received great honor and love from him.

[AD 418] Pelagius on Romans 4:2
If Abraham was justified because of his circumcision, then God gave him nothing and he could have gloried in what he did to himself. Or it may mean that if Abraham carried out the ordinances, he had glory in his own eyes but not in God’s.

[AD 430] Augustine of Hippo on Romans 4:2
Since Abraham without the law obtained glory not by the works of the law (as if he could fulfill the law in his own strength), since the law had not yet been given, the glory belongs to God, not to him. For he was justified not by his own merit, as if by works, but by the grace of God through faith.

[AD 444] Cyril of Alexandria on Romans 4:2
What can we say to those who insist that Abraham was justified by works because he was ready to sacrifice his son Isaac on the altar? Abraham was already an old man when God promised him that he would have a son and that his descendants would be as countless as the stars of the sky. Abraham piously believed that all things are possible with God and so exercised this faith. God reckoned him to be righteous on this account and gave Abraham a reward worthy of such a godly mind, viz., the forgiveness of his previous sins.… So even if Abraham was also justified by his willingness to sacrifice Isaac, this must be regarded as an evident demonstration of a faith which was already very strong.

[AD 458] Theodoret of Cyrus on Romans 4:2
The accomplishment of good works honors those who do them, but it does not reveal the kindness of God. Faith, on the other hand, reveals both the love for God of the one who believes and God’s kindness.