But if our unrighteousness, etc. Though this is a digression from the main subject, it was yet necessary for the Apostle to introduce it, lest he should seem to give to the ill-disposed an occasion to speak evil, which he knew would be readily laid hold on by them. For since they were watching for every opportunity to defame the gospel, they had, in the testimony of David, what they might have taken for the purpose of founding a calumny, -- "If God seeks nothing else, but to be glorified by men, why does he punish them, when they offend, since by offending they glorify him? Without cause then surely is he offended, if he derives the reason of his displeasure from that by which he is glorified." There is, indeed, no doubt, but that this was an ordinary, and everywhere a common calumny, as it will presently appear. Hence Paul could not have covertly passed it by; but that no one should think that he expressed the sentiments of his own mind, he premises that he assumes the person of the ungodly; and at the same time, he sharply, touches, by a single expression, on human reason; whose work, as he intimates, is ever to bark against the wisdom of God; for he says not, "according to the ungodly," but "according to man," or as man. And thus indeed it is, for all the mysteries of God are paradoxes to the flesh: and at the same tine it possesses so much audacity, that it fears not to oppose them and insolently to assail what it cannot comprehend. We are hence reminded, that if we desire to become capable of understanding them, we must especially labor to become freed from our own reason, (proprio sensu) and to give up ourselves, and unreservedly to submit to his word. -- The word wrath, taken here for judgment, refers to punishment; as though he said, "Is God unjust, who punishes those sins which set forth his righteousness?"

But if our unrighteousness - If our sin. The particular sin which had been specified Romans 3:3 was "unbelief." But the apostle here gives the objection a general form. This is to be regarded as an objection which a Jew might make. The force of it is this:
(1) It had been conceded that some had not believed; that is, had sinned.
(2) but God was true to his promises. Notwithstanding their sin, God's character was the same. Nay,
(3) In the very midst of sin, and as one of the results of it, the character of God, as a just Being, shone out illustriously. The question then was,
(4) If his glory resulted from it; if the effect of all was to show that his character was pure; how could he punish that sin from which his own glory resulted? And this is a question which is often asked by sinners.
Commend - Recommend; show forth; render illustrious.
The righteousness of God - His just and holy character. This was the effect on David's mind, that he saw more clearly the justice of God in his threatenings against sin, in consequence of his own transgression. And if this effect followed, if honor was thus done to God, the question was, how he could consistently punish what tended to promote his own glory?
What shall we say? - What follows? or, what is the inference? This is a mode of speech as if the objector hesitated about expressing an inference which would seem to follow, but which was horrible in its character.
Is God unrighteous? - The meaning of this would be better expressed thus: "Is "not" God unrighteous in punishing? Does it not follow that if God is honored by sin, that it would be wrong for him to inflict punishment?"
Who taketh vengeance - The meaning of this is simply, "who inflicts punishment." The idea of vengeance is not necessarily in the original ὀργήν orgēn. It is commonly rendered "wrath," but it often means simply "punishment," without any reference to the state of the mind of him who inflicts it, Matthew 3:7; Luke 3:7; Luke 21:23; John 3:36. Notes, Romans 1:18; Romans 4:15.
I speak as a man - I speak after the manner of human beings. I speak as appears to be the case to human view; or as would strike the human mind. It does not mean that the language was such as wicked people were accustomed to use; but that the objector expressed a sentiment which to human view would seem to follow from what had been said. This I regard as the language of an objector. It implies a degree of reverence for the character of God, and a seeming unwillingness to state an objection which seemed to be dishonorable to God, but which nevertheless pressed itself so strong on the mind as to appear irresistible. No way of stating the objection could have been more artful or impressive.

Jew. But if our unrighteousness commend the righteousness of God - May we not suppose that our unrighteousness may serve to commend and illustrate the mercy of God in keeping and fulfilling to us the promise which he made to our forefathers? The more wicked we are, the more his faithfulness to his ancient promise is to be admired. And if so, would not God appear unjust in taking vengeance and casting us off?
I speak as a man - I feel for the situation both of myself and my countrymen, and it is natural for one to speak as I do.

(2) But if our (g) unrighteousness commend the righteousness of God, what shall we say? [Is] God unrighteous who taketh vengeance? (I speak as (h) a man)
(2) Another objection resulting from the former answer: that the justice of God is commended and set forth by our unrighteousness in such a way that God does not therefore forget that he is the judge of the world, and therefore a most severe avenger of unrighteousness.
(g) Treachery, and all the fruits of it.
(h) Therefore I do not speak these words of my own accord, as though this is what I thought, but this is the talk of man's wisdom, which is not subject to the will of God.

But if our unrighteousness commend the righteousness of God,.... Hence it appears, that the unrighteousness of men commends the righteousness, or faithfulness of God; and yet all unrighteousness is sin; the wrath of God is revealed against it; and would exclude from heaven, were it not for pardon through the blood of Christ; and besides, the one is contrary to the other, and of itself, of its own nature, cannot influence and affect the other: wherefore this can only be understood of the manifestation and illustration of, the righteousness of God by it; which is covered and commended, in punishing the unrighteousness of men; in setting forth Christ to be a propitiation for sin; and in fulfilling his promises, notwithstanding the failings of his people, of which the case of David is a pregnant proof; just as the love of God is illustrated and commended, by the consideration of the sins of men, for whom Christ died, and his grace and mercy in the conversion of them: but if this be true,
what shall we say? shall we allow the following question to be put? this answers to , "what is there to say", or "to be said?" a way of speaking, often used by the Talmudists (n):
is God unrighteous, who taketh vengeance? if the premises are true, this is a just consequence of them; whereas God does take vengeance on men for their unrighteousness, both here and hereafter, it must be a piece of unrighteousness in him so to do; since that for which he takes vengeance on them commends his own righteousness; but that you may know as well by what follows, that this is not an inference of his own, but another's, he adds,
I speak as a man; , "according to the language of the children of men", a phrase often used by the Jewish doctors (o). The apostle did not speak the sentiments of his own mind, he represented another man, and spoke in the language of an adversary.
(n) T. Bab. Bava Bathra, fol. 4. 1. & passim. (o) T. Bab. Ceritot, fol. 11. 1. & passim.

But if, &c.--Another objection: "It would appear, then, that the more faithless we are, so much the more illustrious will the fidelity of God appear; and in that case, for Him to take vengeance on us for our unfaithfulness would be (to speak as men profanely do) unrighteousness in God."
Answer:

But if our unrighteousness commendeth the righteousness of God, etc. Here is presented the Jews' third objection to the conclusion that Israel is under judgment for sin. Paul has just shown that God's righteousness is shown forth in condemning the Jews for their unbelief. "But," says the Jew, "if our unrighteousness demonstrates God's faithfulness, when he condemns us for unbelief, is it right that we should be punished? Our sin gives occasion for God's holiness to be shown forth. Why, then, should we be punished for furnishing such an occasion? Speaking after the manner of men, is not God unrighteous, when he sends wrath on our nation for its unbelief?" God forbid. Rather, "By no means."
How shall God judge the world? How, if no sin is punished which God turns to some good purpose, shall he judge all men according to their deeds?
Why yet am I also judged as a sinner? Here the Jew is supposed to repeat the last objection in another form. "God's truth is shown by our lie. His threatenings are demonstrated to be absolutely true by his rejection of the Jewish nation. If our lie, our false life, has thus shown forth his glory, why should we be individually condemned?" Let us do evil that good may come. The apostle replies to this argument with a reductio ad absurdum. This amounts to saying, "Do evil that good may come," an abominable doctrine, slanderously charged upon Paul by enemies, would justify every iniquity. This doctrine, so strongly condemned, has been taught by the Jesuits.
Whose damnation is just. All who teach such doctrine are justly condemned.
Are we better than they? If Jews shall be judged as well as Gentiles, are not we Jews, having the oracles of God, better than they, and hence likely to be justified? The Jew is still supposed to be speaking. To this Paul replies, In no wise, for he had already shown (chapters 1 and 2) that both Jews and Gentiles were sinners before God.

But, it may be farther objected, if our unrighteousness be subservient to God's glory, is it not unjust in him to punish us for it? I speak as a man - As human weakness would be apt to speak.