According to John Chrysostom, "the Apostle acts thus so that he may not close the path to faith for the Jews by casting them into despair. Nor does he give those who believed from the Gentiles occasion for high-mindedness, lest they too, becoming proud, suffer loss in the faith.
The Apostle's aim is to destroy high-mindedness in the believing Gentiles, and to suggest to the Jews that they have not fallen completely. For as the Gentiles, having learned modesty, will remain more securely in the faith, so the Jews, brought out of despair, will more readily approach grace."
Explaining the words, "through their fall salvation has come to the Gentiles," St. John Chrysostom says: "These are not Paul's words alone. The parables in the Gospels have the same meaning.
He who made a wedding feast for his son began to call people from the crossroads when those invited refused to come (Mt 22:9). He who planted a vineyard then resolved to give it to other vinedressers when the first killed the heir (Mt 21:38).
The Lord Jesus came to the Jews. Yet despite the great multitude of miracles He performed, they did not receive Him and crucified Him. After this He began to draw the Gentiles to Himself.
By the honor shown to them, He wounded the insensible Jews and persuaded them through mutual emulation to come to Him."
As a faithful messenger of God, the Apostle himself also strives to awaken in all the same spirit of emulation, as he himself testifies in verses 13 and 14.
According to John Chrysostom, he does the same in verse 12, for "here also the Apostle says something pleasing to the Jews. He encourages those of them who have fallen, proving abundantly that they can hope for salvation if they change.
If, he says, so many received salvation when they stumbled, and so many received salvation when they were rejected, then consider what will happen when they turn back. For he did not say, how much more their conversion, or their change, or their correction.
Rather, he said, how much more their fullness, that is, when all come to Christ. By this he indicates that then there will be a greater or full measure of God's grace."
As though continuing this thought, blessed Theodoret writes: "If, says the Apostle, even when they, the Jews, did not believe, the Gentiles were received and freed from their former ignorance, then it is clear that, if they wished to believe, nothing else would remain to be accomplished except the resurrection of the dead.
The Lord also said this: 'And this Gospel of the Kingdom will be preached among all nations as a testimony to them; and then the end will come'" (Mt 24:14).