Romans 11:12

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 ) ( 2 Corinthians 5:19 ) ( 1 John 2:2 ) ; 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.