What he means is somewhat as follows. Pharaoh was a vessel of wrath, that is, a man who by his own hard-heartedness had kindled the wrath of God. For after enjoying much long-suffering, he became no better, but remained unimproved. Wherefore he calls him not only "a vessel of wrath," but also one "fitted for destruction." That is, fully fitted indeed, but by his own proper self. For neither had God left out anything of the things likely to recover him, nor did he leave out anything of those that would ruin him, and put him beyond any forgiveness. Yet still, though God knew this, "He endured him with much long-suffering," being willing to bring him to repentance. For had He not willed this, then He would not have been thus long-suffering. But as he would not use the long-suffering in order to repentance, but fully fitted himself for wrath, He used him for the correction of others, through the punishment inflicted upon him making them better, and in this way setting forth His power. For that it is not God's wish that His power be so made known, but in another way, by His benefits, namely, and kindnesses, he had shown above in all possible ways. For if Paul does not wish to appear powerful in this way ("not that we should appear approved," he says, "but that you should do that which is honest,") [2 Corinthians 13:7], much less does God. But after that he had shown long-suffering, that He might lead to repentance, but he did not repent, He suffered him a long time, that He might display at once His goodness and His power, even if that man were not minded to gain anything from this great long-suffering. As then by punishing this man, who continued incorrigible, He showed His power, so by having pitied those who had done many sins but repented, He manifested His love toward man. But it does not say, love towards man, but glory, to show that this is especially God's glory, and for this He was above all things earnest. But in saying, "which He had afore prepared unto glory," he does not mean that all is God's doing. Since if this were so, there were nothing to hinder all men from being saved. But he is setting forth again His foreknowledge, and doing away with the difference between the Jews and the Gentiles. And on this topic again he grounds a defense of his statement, which is no small one. For it was not in the case of the Jews only that some men perished, and some were saved, but with the Gentiles also this was the case. Wherefore he does not say, all the Gentiles, but, "of the Gentiles," nor, all the Jews, but, "of the Jews." As then Pharaoh became a vessel of wrath by his own lawlessness, so did these become vessels of mercy by their own readiness to obey. For though the more part is of God, still they also have contributed themselves some little. Whence he does not say either, vessels of well-doing, or vessels of boldness (παρρησίας), but "vessels of mercy," to show that the whole is of God. For the phrase, "it is not of him that wills, nor of him that runs," even if it comes in the course of the objection, still, were it said by Paul, would create no difficulty. Because when he says, "it is not of him that wills, nor of him that runs," he does not deprive us of free-will, but shows that all is not one's own, for that it requires grace from above. For it is binding on us to will, and also to run: but to confide not in our own labors, but in the love of God toward man. And this he has expressed elsewhere. "Yet not I, but the grace which was with me." [1 Corinthians 15:10] And he well says, "Which He had afore prepared unto glory." For since they reproached them with this, that they were saved by grace, and thought to make them ashamed, he far more than sets aside this insinuation. For if the thing brought glory even to God, much more to them through whom God was glorified. But observe his forbearance, and unspeakable wisdom. For when he had it in his power to adduce, as an instance of those punished, not Pharaoh, but such of the Jews as had sinned, and so make his discourse much clearer, and show that where there were the same fathers, and the same sins, some perished, and some had mercy shown them, and persuade them not to be doubtful-minded, even if some of the Gentiles were saved, while the Jews were perishing; that he might not make his discourse irksome, the showing forth of the punishment he draws from the foreigner, so that he may not be forced to call them "vessels of wrath." But those that obtained mercy he draws from the people of the Jews. And besides, he also has spoken in a sufficient way in God's behalf, because though He knew very well that the nation was fitting itself as a vessel of destruction, still He contributed all on His part, His patience, His long-suffering, and that not merely long-suffering, but "much long-suffering;" yet still he was not minded to state it barely against the Jews. Whence then are some vessels of wrath, and some of mercy? Of their own free choice. God, however, being very good, shows the same kindness to both. For it was not those in a state of salvation only to whom He showed mercy, but also Pharaoh, as far as His part went. For of the same long-suffering, both they and he had the advantage. And if he was not saved, it was quite owing to his own will: since, as for what concerns God, he had as much done for him as they who were saved. Having then given to the question that answer which was furnished by facts, in order to give his discourse the advantage of other testimony in its favor, he introduces the prophets also making the same declarations aforetime. For Hosea, he says, of old put this in writing, as follows:
This means that we should not be lukewarm in doing God’s work or the law, as God says in the Revelation of John: “Because you are lukewarm, I shall spit you out of my mouth.” Daily meditation removes laziness and makes people vigilant.
For this also genders love when with honor we also show a readiness to protect: as there is nothing that makes men beloved so much as honor and forethought. For to love is not enough, but there must be this also: or rather this also comes of loving, as also loving has its warmth from this, and they are confirmative one of another. For there are many that love in mind, yet reach not forth the hand. And this is why he uses every means to build up love. And how are we to become "not backward in zeal?"
"Fervent in spirit." See how in every instance he aims after higher degrees; for he does not say "give" only, but "with largeness;" nor "rule," but do it "with diligence;" nor "show mercy," but do it "with cheerfulness;" nor "honor," but "prefer one another;" nor "love," but do it "without dissimulation;" nor refrain from "evil" things, but "hate" them; nor hold to "what is good," but "cleave" to it; nor "love," but to do it "with brotherly affection;" nor be zealous, but be so without backwardness; nor have the "Spirit," but have it "fervent," that is, that you may be warm and awakened. For if you have those things aforesaid, you will draw the Spirit to you. And if This abide with you, It will likewise make you good for those purposes, and all things will be easy from the Spirit and the love, while you are made to glow from both sides. Do you not see the bulls (Hannibal. ap. Liv. xxii. 16) that carry a flame upon their back, how nobody is able to withstand them? So thou also will be more than the devil can sustain, if you take both these flames. "Serving the Lord." For it is possible to serve God in all these ways; in that whatever you do to your brother passes on to your Master, and as having been Himself benefited, He will reckon your reward accordingly. See to what height he has raised the spirit of the man that works these things! Then to show how the flame of the Spirit might be kindled, he says,
Love by itself is not enough; there must be zeal as well. For zeal also comes out of loving and gives it warmth, so that the one confirms the other. For there are many who have love in their mind but who do not stretch out their hand. This is why Paul calls on every means he knows to build up love.
Do not become slow and lazy in God’s work out of concern for the world. The Lord does not love those who are unresponsive and is nauseated by those who are lukewarm. If we are resistant to the world we then manifestly glow with the Spirit, doing all things not for the world or its vices but for the Lord.
Spirit is the word Paul uses here for “grace.” … He does the same thing elsewhere when he says: “Do not quench the Spirit.” The Spirit is quenched in those who are unworthy of grace.
[AD 407] John Chrysostom on Romans 9:22-23:24