Now what is this to the branches that are cut off? Nothing. For, as I said before, while seeming to devise a sort of weak shadow of consolation, and in the very midst of his aiming at the Gentile, he gives them a mortal blow; for by saying, “boast not against them,” and, “if you boast, you bear not the root,” he has shown the Jew that the things done deserved boasting of, even if it was not right to boast, thus at once rousing him and provoking him to faith, and smiting at him, in the attitude of an advocate, and pointing out to him the punishment he was undergoing, and that other men had possession of what were their goods.
Ver. 19. “You will say then,” he goes on, “The branches were broken off that I might be grafted in.”
Again he establishes, by way of objection, the opposite to the former position, to show that what he said before, he had not said as directly belonging to the subject, but to draw them to him. For it was no longer by their fall that salvation came to the Gentiles, nor was it their fall that was the riches of the world. Nor was it by this that we were saved, because they had fallen, but the reverse. And he shows that the providence in regard to the Gentiles was a main object, even though he seems to put what he says into another form. And the whole passage is a tissue of objections, in which he clears himself of the suspicion of hatred, and makes his language such as will be acceptable.
Ver. 20. “Well,” he praises what they said, then he alarms them again by saying, “Because of unbelief they were broken off, and you are grafted in by faith.”
So here another encomium, and for the other party an accusation. But he again lays their pride low by proceeding to say, “be not high-minded, but fear.” For the thing is not matter of nature, but of belief and unbelief. And he seems to be again bridling the Gentile, but he is teaching the Jew that it is not right to cling to a natural kinsmanship. Hence he goes on with, “Be not high-minded,” and he does not say, but be humble, but, fear. For haughtiness genders a contempt and listlessness. Then as he is going into all the sorrows of their calamity, in order to make the statement less offensive, he states it in the way of a rebuke given to the other as follows:
Ver. 21. “For if God spared not the natural branches,” and then he does not say, neither will He spare you, but “take heed, lest He also spare not you.” So paring (ὑ ποτεμνόμενος) away the distasteful from his statement, representing the believer as in the struggle, he at once draws the others to him, and humbles these also.
Ver. 22. “Behold therefore the goodness and severity of God: on them which fell, severity; but toward you, goodness, if you continue in His goodness: otherwise thou also shall be cut off.”
And he does not say, Behold your well doing, behold your labors, but, “Behold the goodness of God” toward man, to show that the whole comes of grace from above, and to make us tremble. For this reason for boasting should make you to fear: since the Lord (δεσπότης) has been good unto you, do thou therefore fear. For the blessings do not abide by you unmovable if you turn listless, as neither do the evils with them, if they alter; “For thou also,” he says, “unless thou continue in the faith, will be cut off.”
Ver. 23. “And they also, if they abide not in unbelief, shall be grafted in.”
For it was not God that cut them off, but they have broken themselves off and fallen, and he did well to say have broken themselves off. For He has never yet so (Sav. conj. manuscript corr. οὗτος) cast them off, though they have sinned so much and so often. You see what a great thing a man's free choice is, how great the efficacy of the mind is. For none of these things is immutable, neither your good nor his evil. You see too how he raises up even him in his despondency, and humbles the other in his confidence; and do not thou be faint at hearing of severity, nor thou be confident at hearing of goodness. The reason why He cut you off in severity was, that you might long to come back. The reason why He showed goodness to you was, that you might continue in (he does not say the faith, but) His goodness, that is, if you do things worthy of God's love toward man. For there is need of something more than faith. You see how he suffers neither these to lie low, nor those to be elated, but he also provokes them to jealousy, by giving through them a power to the Jew to be set again in this one's place, as he also had first taken the other's ground. And the Gentile he put in fear by the Jews, and what had happened to them, lest they should feel elated over it. But the Jew he tries to encourage by what had been afforded to the Greek. For thou also, he says, will be cut off if you grow listless, (for the Jew was cut off), and he will be grafted in if he be earnest, for thou also wast grafted in. But it is very judicious in him to direct all he says to the Gentile, as he is always in the habit of doing, correcting the feeble by rebuking the stronger. This he does in the end of this Epistle too, when he is speaking of the observance of meats. Then, he grounds this on what had already happened, not upon what was to come only. And this was more likely to persuade his hearer. And as he means to enter on consecutiveness of reasonings, such as could not be spoken against, he first uses a demonstration drawn from the power of God. For if they were cut off, and cast aside, and others took precedence of them in what was theirs, still even now despair not.
“For God is able,” he says, “to graft them in again,” since He does things beyond expectation. But if you wish for things to be in order, and reasons to be consecutive, you have from yourselves a demonstration which more than meets your wants.
Ver. 24. “For if you were cut out of the olive tree, which is wild by nature, and were grafted contrary to nature into a good olive tree, how much more shall these, which be the natural branches, be grafted into their own olive tree.”
Source: Homilies on Romans (New Advent)