And if their fall, etc. As he had taught us that after the Jews were repudiated, the Gentiles were introduced in their place, that he might not make the salvation of the Jews to be disliked by the Gentiles, as though their salvation depended on the ruin of the Jews, he anticipates this false notion, and lays down a sentiment of an opposite kind, that nothing would conduce more to advance the salvation of the Gentiles, than that the grace of God should flourish and abound among the Jews. To prove this, he derives an argument from the less, -- "If their fall had raised the Gentiles, and their diminution had enriched them, how much more their fullness?" for the first was done contrary to nature, and the last will be done according to a natural order of things. And it is no objection to this reasoning, that the word of God had flowed to the Gentiles, after the Jews had rejected, and, as it were, cast it from them; for if they had received it, their faith would have brought forth much more fruit than their unbelief had occasioned; for the truth of God would have been thereby confirmed by being accomplished in them, and they also themselves would have led many by their teaching, whom they, on the contrary, by their perverseness, had turned aside. Now he would have spoken more strictly correct, if, to the fall, he had opposed rising: [1] of this I remind you, that no one may expect here an adorned language, and may not be offended with this simple mode of speaking; for these things were written to mold the heart and not the tongue.

Footnotes

1 - This is not quite correct: the first part is a mere announcement of a fact -- the fall of the Jews; and then in what follows, according to the usual style of Scripture, the same thing is stated in other words, and a corresponding clause is added; and the antithesis is found to be suitable -- the diminution and the completion. The reason for the restatement of the first clause seems to be this, -- that the fall might not be deemed as total, but in part; it was hettema, a less part, a diminution, a lessening of their number in God's kingdom. A contrast to this is the pleroma, the full or complete portion, that is, their complete restoration, as it is said in Romans 11:26. To preserve the antithesis, the first word must have its literal meaning, a diminution or lessening, that is, as to the number saved. Hammond renders the phrase, "their paucity." -- Ed.

If the fall of them - If their lapse, or falling. If their temporal rejection and being cast off for a time has already accomplished so much.
Be the riches of the world - The word "riches" means wealth, abundance of property; more than is necessary to the supply of our needs. Hence, it means also anything that may promote our comfort or happiness, as wealth is the means of securing our welfare. The gospel is called riches, as it is the means of our highest enjoyment, and eternal welfare. It is the means of conferring numberless spiritual blessings on the Gentile world; and as this was done by the fall of the Jews, so it could be said that their fall was the riches of the world. It was the occasion or means without which the blessings of the gospel could not be conferred on the world.
The diminishing of them - Margin, "Decay." "Loss" ἥττημα hēttēma. This word means diminution, defect, what is lacked or missing. Hence, also judgment, condemnation. Here it means their degradation; the withdrawing of their special privileges; their rejection. It stands opposed to "their fulness."
The riches of the Gentiles - The means of conferring important blessings on the Gentiles.
How much more their fulness - The word "fulness" πλήρωμα plērōma means what fills up, or completes anything. Thus, it is applied to what fills a vessel or cup; also to the piece of cloth which is put in to fill up the rent in a garment; Matthew 9:16. To the fragments which were left when Christ had fed the five thousand; Mark 8:20; Romans 13:10. "Love is the fulfilling of the law," that is, it is the filling up of the law, or what renders the obedience complete; see Galatians 5:14. Here it stands opposed to their fall, and their diminution, and evidently means their complete restoration to the favor of God; their recovery from unbelief and apostasy. That there will be such a recovery, the apostle proceeds to show. The sentiment of the passage then is, If their rejection and punishment; their being cut off from the favor of God, an event apparently so unlikely to promote the spread of true religion, if their being withrawn from all active influence in spreading the true knowledge of God, be yet the occasion of so many blessings to mankind as have attended the spread of the gospel in consequence of it; how much more shall we expect when they shall be restored; when the energy and zeal of the Jewish nation shall unite with the efforts of others in spreading the knowledge of the true Messiah. In what way, or when, this shall be, we know not. But it is easy to see, that if the Jewish people should be converted to the Christian faith, they would have facilities for spreading the truth, which the church has never had without them.
(1) they are scattered in all nations, and have access to all people.
(2) their conversion, after so long unbelief, would have all the power and influence of a miracle performed in view of all nations. It would be seen why they had been preserved, and their conversion would be a most striking fulfillment of the prophecies.
(3) they are familiar with the languages of the world, and their conversion would at once establish many Christian missionaries in the heart of all the kingdoms of the world. It would be kindling at once a thousand lights in all the dark parts of the earth.
(4) the Jews have shown that they are eminently suited to spread the true religion. It was by Jews converted to Christianity, that the gospel was first spread. Each of the apostles was a Jew; and they have lost none of the ardor, enterprise, and zeal that always characterized their nation. Their conversion would be, therefore, to give to the church a host of missionaries prepared for their work, familiar with all customs, languages, and climes, and already in the heart of all kingdoms, and with facilities for their work in advance, which others must gain only by the slow toil of many years.

Now if the fall of them - The English reader may imagine that, because fall is used in both these verses, the original word is the same. But their fall, and the fall of them, is παραπτωμα, the same word which we render offense, Romans 5:15, Romans 5:17, Romans 5:18, and might be rendered lapse. Whereas that they should fall (Romans 11:11) is, ινα πεσωσι. Now, πιπτω, to fall, is used in a sense so very emphatical as to signify being slain. So Homer, Il. viii., ver. 475.
Ηματι τῳ, οτ' αν οἱ μεν επι πρυμνησι μαχωνται,
Στεινει εν αινοτατῳ, περι Πατροκλοιο πεσοντος
Ὡς γαρ θεσφατον εστι.
And for Patroclus slain, the crowded hosts,
In narrow space, shall at the ships contend.
Such the divine decree.
And again, Il. xi., ver. 84.
Οφρα μεν ηως ην και αεξετο ἱερον ημαρ,
Τοφρα μαλ' αμφοτερων βελε' ἡπτετο, πιπτε δε λαος.
While morning lasted, and the light of day
Increased, so long the weapons on both sides
Flew in thick vollies; and the people fell.
Cowper.
It is well known, that to fall in battle means to be killed. It is in such a sense as this that St. Paul used the word fall, when he says, Have they stumbled that they should Fall? He means a fall quite destructive and ruinous; whereas by their fall, and the fall of them, he means no more than such a lapse as was recoverable; as in the case of Adam's offense. See Dr. Taylor.
The riches of the world - If, in consequence of their unbelief, the riches of God's grace and goodness be poured out on the whole Gentile world, how much more shall that dispensation of grace and mercy enrich and aggrandize the Gentiles, which shall bring the whole body of the Jews to the faith of the Gospel! Here the apostle supposes, or rather predicts, that such a dispensation shall take place; and that, therefore, the Jews have not so stumbled as to be finally irrecoverable.

Now if the fall of them [be] the (k) riches of the world, and the diminishing of them the riches of the Gentiles; how much more their (l) fulness?
(k) By "riches" he means the knowledge of the Gospel to everlasting life: and by the "world", all nations dispersed throughout the whole world.
(l) Of the Jews, when the whole nation without exception will come to Christ.

Now if the fall of them be the riches of the world,.... By "the world", as is clear from the next clause, is meant the Gentiles; who were frequently called so by the Jews, who reckoned themselves to be "the church", and all the nations round about them, "the world"; which observation may serve to illustrate other passages of Scripture; see John 3:16; now the fall of the Jews, which was a lessening of them, was the riches of the Gentiles;
and the diminishing of them the riches of the Gentiles; the number of the true believers in Christ among them were very few, the generality of them received him not, but stumbled at him, and fell through unbelief; but the few that did believe were the means of carrying and spreading the Gospel, which is, "the unsearchable riches of Christ", Ephesians 3:8, in the Gentile world: thus at first a persecution being raised against the church at Jerusalem, the ministers of the Gospel were scattered abroad, and went everywhere preaching the word; and afterwards the Jews behaving in a very indecent manner towards the apostles of Christ, they turned in a manner wholly to the Gentiles; and thus by the means of a few, a diminutive company, of which the Apostle Paul was one, the Gospel, the pearl of great price, treasure hid in a field, and put into earthen vessels, was carried into the Heathen world, and by it they were enriched. This handful of men that went out of Judea, were the means of converting vast numbers, large multitudes of souls among the Gentiles, which may be also designed by "riches": this word sometimes signifying plenty, see Romans 2:4; and also of enriching them with the gifts and graces of the Spirit, and of directing them to Christ, who has durable riches, treasures of wisdom and knowledge, riches of grace, and riches of glory. Now the apostle argues, that if such a small number of the Jews who embraced Christ, were of so much advantage to the Gentiles,
how much more their fulness? when converts to Christ among them will be as the sand of the sea, a nation of them shall be born again at once, and all Israel be saved. This will be a great accession to the Gentile church, bring much glory to it, contribute greatly to its welfare, and be a means of establishing their faith, and of putting fresh life and vigour into them, and of inspiring them with more zeal for Christ, and for his honour and glory.

Now if the fall of them--"But if their trespass," or "false step"
be the riches of the--Gentile
world--as being the occasion of their accession to Christ.
and the diminishing of them--that is, the reduction of the true Israel to so small a remnant.
the riches of the Gentiles; how much more their fulness!--that is, their full recovery (see on Romans 11:26); that is, "If an event so untoward as Israel's fall was the occasion of such unspeakable good to the Gentile world, of how much greater good may we expect an event so blessed as their full recovery to be productive?"

The first part of this verse is treated of, Romans 11:13, &c; the latter, How much more their fulness, (that is, their full conversion,) Romans 11:23, &c.
So many prophecies refer to this grand event, that it is surprising any Christian can doubt of it. And these are greatly confirmed by the wonderful preservation of the Jews as a distinct people to this day. When it is accomplished, it will be so strong a demonstration, both of the Old and New Testament revelation, as will doubtless convince many thousand Deists, in countries nominally Christian; of whom there will, of course, be increasing multitudes among merely nominal Christians. And this will be a means of swiftly propagating the gospel among Mahometans and Pagans; who would probably have received it long ago, had they conversed only with real Christians.