The interpretation timeline
Romans 11:23 Douay-Rheims

And they also, if they abide not still in unbelief, shall be grafted in: for God is able to graft them in again.

A.D. 407 – 1871 5 witnesses

Patristic

before A.D. 750
407
A.D.
John Chrysostom Patristic
A.D. 347–407
“"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 hath never yet so 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 thy 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 thee off in severity was, that thou mightest long to come back. The reason why He showed goodness to thee was, that thou mightest continue in (he does not say the faith, but) His goodness, that is, if thou do things worthy of God's love toward man. For there is need of something more than faith.”
Source

Scholastic

c. 1100 – 1500
1273
A.D.
Thomas Aquinas Catholic
1225–1274
“After the Apostle has shown that the fall of the Jews was useful and reparable, here he excludes the boasting of the Gentiles against the Jews. And concerning this he does two things. First he shows the converted Gentiles that they ought not to boast against the Jews; second he responds to an objection of the Gentiles, at the place, "Thou wilt say then, the branches were broken off," and so on. Concerning the first he does two things. First he forbids the Gentiles to boast against the Jews; second he assigns the reason for the prohibition, at the place, "for if thou boastest," and so on. Now an occasion for boasting against the Jews seemed to press upon the Gentiles from two directions. First indeed from the defect of the Jews, when he says: it has been said that if the root is holy, the branches also are; but if some of the branches — that is, of the Jews (not all of them, however) — were broken off, that is, divided from the faith of the fathers, who are compared to the root, do not, namely, boast. Job 15: "the flame shall dry up his branches." Wisdom 4: "the unfruitful branches shall be broken." Second, a matter for boasting seems to press upon them from the side of their own promotion. Now the promotion of anyone is wont to lift him up into vain glory all the more, the more he is raised up from a viler condition, according to that word of Proverbs 30: "for three things the earth is disquieted, and for the fourth it cannot bear: for a servant when he reigneth," and so on. And therefore he first sets down the abject condition from which they had been taken up, saying: but thou, a Gentile, when thou wast a wild olive in the condition of Gentility, that is, an unfruitful tree. Jeremiah 17: "they shall be like the tamarisk in the desert." Matthew 3: "every tree that bringeth not forth good fruit shall be cut down," and so on. Then he sets down their promotion. And first indeed as to this, that they were taken up into the dignity of that nation; hence he says, thou art grafted in among them, that is, in their place. Job 34: "he shall break in pieces many and innumerable, and shall make others to stand in their stead." Second, by this, that they are made companions of the patriarchs, whom above he had compared to the root; hence he says, and art made a partaker of the root, that is, thou art made a companion of the patriarchs and the prophets. Matthew 8: "many shall come from the east, and shall sit down with Abraham, Isaac, and Jacob in the kingdom of heaven." Third, by comparison to the glory of the apostles, when he says, and of the fatness of the olive tree. Now the olive tree itself is said to be the nation of the Jews, on account of the rich spiritual fruits which it bore. Jeremiah 11: "the Lord called thy name a plentiful olive tree, fair, fruitful, and beautiful"; Psalm 51: "but I, as a fruitful olive tree in the house of God." Now just as the root of this olive tree are the patriarchs and prophets, so also the fatness of this olive tree is the abundance of the grace of the Holy Spirit, which the apostles had above all others, as the Gloss says. Hence in Judges 9 the olive tree is introduced as saying: "can I leave my fatness?" Psalm 62: "let my soul be filled as with marrow and fatness." Thus, then, the Gentiles were promoted to the fellowship of that people, namely of the patriarchs and apostles and prophets. Ephesians 2: "you are fellow citizens with the saints, and domestics of God, built upon the foundation of the apostles and prophets." And although thou, O Gentile, mayest seem to have these occasions for boasting, do not, nevertheless, boast against the branches, that is, against the Jews. 1 Corinthians 5: "your glorying is not good." Then, when he says, "for if thou boastest," and so on, he assigns the reason for his admonition, saying: for if — this admonition notwithstanding — thou boastest, insulting the Jews whether standing or cut off, consider this, for the repression of thy boasting: that thou bearest not the root, but the root thee, that is, Judea did not receive salvation from Gentility, but rather the reverse. John 4: "salvation is of the Jews." Hence also it was promised to Abraham, Genesis 22, that in him all the kindreds of the earth would be blessed. Then, when he says, "thou wilt say then," and so on, he excludes the objection of the Gentiles. And first he proposes the objection; second he excludes it from a consideration of the divine judgment, at the place, "well," and so on; third he leads them into a diligent consideration of the divine judgments, at the place, "behold therefore the goodness," and so on. He says therefore first: therefore thou, O Gentile, who boastest against the Jews, perhaps sayest: the branches were broken that I might be grafted in, that is, God permitted the Jews to fall away from the faith for this purpose, that I might enter into the faith. But no one endures the detriment of one thing except for the sake of a thing more precious and more beloved, just as a physician permits an infirmity to be in the foot in order that he may heal the eye. Thus, therefore, from this very fact Gentility seems to be more precious and more accepted by God than Judea. Hence in Malachi 1 it is said: "I have no pleasure in you, saith the Lord God of hosts, and I will not receive a gift of your hand. For from the rising of the sun even to the going down, my name is great among the Gentiles." And Isaiah 49: "it is a small thing that thou shouldst be my servant to raise up the tribes of Jacob. I have given thee for a light of the Gentiles." Then, when he says, "well," and so on, he excludes the objection. And first he assigns the cause of the defect of the Jews and of the promotion of the Gentiles, saying: well dost thou say in this, that God permitted the branches to be broken that thou mightest be grafted in, but consider the cause of the breaking of the branches: because of unbelief, I say, they were broken, namely because they were unwilling to believe in Christ. Ezekiel 2: "they are a rebellious and gainsaying people with thee." John 8: "if I say the truth to you, why do you not believe me?" But thou — namely, O Gentile — standest by faith, that is, by believing in Christ, in whom thou hast obtained grace. 2 Corinthians 1: "for by faith you stand." 1 Corinthians 15: "I make known unto you the gospel, wherein you stand, by which also you are saved." Second he adduces an admonition, saying: be not high-minded, that is, do not presume beyond thyself concerning thyself. Below, Romans 12: "not minding high things, but consenting to the humble." Psalm 130: "Lord, my heart is not exalted, nor are my eyes lofty." But fear, lest namely thou too be broken off through unbelief — which pertains to chaste fear. Proverbs 28: "blessed is the man that is always fearful, but he that is hardened in mind shall fall into evil." Ecclesiasticus 1: "the fear of the Lord driveth out sin." Third he assigns the reason for his admonition, saying: for if God hath not spared the natural branches, that is, the Jews, who descended by natural origin from the patriarchs, so as to permit them to be broken off, fear lest perhaps he spare not thee either — that is, lest he permit thee to fall away through unbelief. Proverbs 6: "the jealousy and rage of a man will not spare in the day of revenge." Jeremiah 13: "I will not spare, nor have I pity, so that I do not disperse them." In this, therefore, consists the Apostle's solution: that when someone sees himself to have obtained grace while another falls, he ought not to be puffed up against the one who falls, but rather to fear for himself, because pride itself is the cause of ruin, and fear is the cause of custody and caution. Then, when he says, "behold therefore the goodness and the severity," and so on, he leads them into a diligent consideration of the divine judgments. And first he leads them to consider; second he instructs them, as though they were not able to consider by themselves, at the place, "for I would not have you ignorant, brethren," and so on; third, as though he himself were not fully sufficient for the investigation of these things, he exclaims in admiration of the divine wisdom, at the place, "O the depth of the riches," and so on. Concerning the first he does three things. First he shows what ought to be considered, saying: behold therefore — that is, diligently consider — the goodness of God, showing mercy; Psalm 72: "how good is God to Israel, to them that are of a right heart"; above, chapter 2: "or despisest thou the riches of his goodness?" And the severity, of him punishing; Psalm 93: "the Lord is the God of revenge." Nahum 1: "God is jealous, and the Lord revengeth." For the first consideration bestows hope; the second, fear, so that despair and presumption may be avoided. Second he shows in whom each of the aforesaid things is to be considered with respect to what was said, saying: on them indeed, namely the Jews, who fell, severity — Lamentations 2: "the Lord hath cast down, and hath not spared, he hath destroyed all that was beautiful in Jacob" — but towards thee, namely the Gentile who art grafted in, goodness. Psalm 118: "thou hast done goodness with thy servant, O Lord." Third he shows in what manner these things can be considered in the aforesaid, because not immovably, as something that can change in the future. And first he shows this with respect to the Gentiles, saying: in thee, I say, behold the goodness of God working, yet on this condition, if thou continue in his goodness. John 15: "abide in my love." Otherwise, if thou do not take pains to persevere through fear and humility, thou also shalt be cut off. Matthew 3: "every tree that bringeth not forth good fruit shall be cut down." Second he shows the same with respect to the Jews, and first he proposes what he intends, saying: and they also, namely the Jews, if they shall not abide still in unbelief, shall be grafted in, that is, they shall be restored to their own condition. Jeremiah 3: "thou hast played the harlot with many lovers, nevertheless return to me, saith the Lord." Second he proves what he had said, and first, from the divine power, saying: for God is able to graft them in again; and therefore one must not despair of their salvation. Isaiah 59: "behold the hand of the Lord is not shortened, that it cannot save." Second he proves the same by an argument from the lesser, saying: for if thou, O Gentile, wert cut out of the wild olive tree which was natural to thee, that is, out of Gentility, which was naturally unfruitful — not indeed as the Lord made nature, but as it has been corrupted through sin. Wisdom 12: "their nation is wicked, and their malice is natural." Ephesians 2: "we were by nature children of wrath" — and wert grafted, contrary to nature, into the good olive tree, that is, into the faith of the Jews, that is, contrary to the common course of nature (for it is not the custom for a branch of a bad tree to be grafted into a good tree, but rather the reverse). Now that which God does is not contrary to nature, but is simply natural. For we call that natural which is done by an agent to whom the patient is naturally subject, even though it may not be according to the patient's own particular nature; just as the flux and reflux of the sea is natural, on account of the fact that it is caused by the motion of the moon, to which water is naturally subject, although it is not natural according to the form of water. So too, since every creature is naturally subject to God, whatever God does in a creature is simply natural, although perhaps it is not natural according to the proper and particular nature of the thing in which it is done — as, for instance, when a blind man is given light and a dead man is raised. If, I say, this was done contrary to nature, how much more shall these, who are according to nature, that is, who belong to the nation of the Jews by natural origin, be grafted into their own olive tree, that is, be brought back to the dignity of their own nation. Malachi, last chapter: "he shall turn the hearts of the fathers to the children, and the hearts of the children to their fathers."”

Post-Reformation

c. 1650 – 1900
1771
A.D.
John Gill Reformed
1697–1771
“And they also, if they abide not still in unbelief,.... The apostle suggests that the Jews also might be recovered and brought into a Gospel church state, provided they did not continue in infidelity; but inasmuch as they seem to lie under invincible ignorance, obstinacy, and unbelief, and were such bitter enemies to the Gospel, and abhorrers of Gospel ordinances, and a Gospel church state; yea, that they must and will abide in unbelief, unless the Spirit of God convinces them of it, and it is given to them to believe in Christ, and they are powerfully drawn by the Father to come to the Son, there is no possibility or likelihood that they shall be grafted in, or taken into a Gospel church state; to which the apostle answers, and argues for their ingrafting, and the possibility of it from the power of God: for God is able to graft them in again; as many of them were in the times of the apostles, and some since, for nothing is impossible with God; he can remove their unbelief, knock off the shackles and fetters in which they are held, and bring, them out of the prison of infidelity, in which they are shut up; he is able to take away the blindness of their minds, and the hardness of their hearts, the veil that is over them, and turn them to the Lord; he can by his mighty power work faith in them, and cause them to look on him whom they have pierced, and mourn in an evangelical manner; he can bring them to Christ, and into his churches, and among his people, and fold them with the rest of his sheep; so that there one fold of Jew and Gentile, under one shepherd, Jesus Christ.”
Source
1832
A.D.
Adam Clarke Methodist
1762–1832
“If they abide not in unbelief - So, we find that their rejection took place in consequence of their wilful obstinacy: and, that they may return into the fold, the door of which still stands open. For God is able to graft them in again - Fallen as they are and degraded, God can, in the course of his providence and mercy, restore them to all their forfeited privileges; and this will take place if they abide not in unbelief: which intimates that God has furnished them with all the power and means necessary for faith, and that they may believe on the Lord Jesus whenever they will. The veil now continues on their heart; but it is not a veil which God has spread there, but a veil occasioned by their own voluntary and obstinate unbelief: and, when they shall turn to the Lord, (Jesus), the veil shall be taken away. See what the apostle has said, Co2 3:6-18.”
Source
1871
A.D.
1871
“And they also--"Yea, and they" if they abide not still in unbelief, shall be grafted in: for God is able to graft them in again--This appeal to the power of God to effect the recovery of His ancient people implies the vast difficulty of it--which all who have ever labored for the conversion of the Jews are made depressingly to feel. That intelligent expositors should think that this was meant of individual Jews, reintroduced from time to time into the family of God on their believing on the Lord Jesus, is surprising; and yet those who deny the national recovery of Israel must and do so interpret the apostle. But this is to confound the two things which the apostle carefully distinguishes. Individual Jews have been at all times admissible, and have been admitted, to the Church through the gate of faith in the Lord Jesus. This is the "remnant, even at this present time, according to the election of grace," of which the apostle, in the first part of the chapter, had cited himself as one. But here he manifestly speaks of something not then existing, but to be looked forward to as a great future event in the economy of God, the reingrafting of the nation as such, when they "abide not in unbelief." And though this is here spoken of merely as a supposition (if their unbelief shall cease)--in order to set it over against the other supposition, of what will happen to the Gentiles if they shall not abide in the faith--the supposition is turned into an explicit prediction in the verses following.”
Source
Modern · 1953 →

The in-app commentary runs from the Fathers to the early-modern record, then stops — that's where the public-domain sources end, not where the reading does. For the modern reading, follow the sources directly.