Romans 11:18

It displeases God if someone rejoices at the misfortune of others, as Solomon says. In any case, the Jews were not rejected for the sake of the Gentiles. Rather, it was because they were rejected that they gave an opportunity for the gospel to be preached to the Gentiles. If you boast against those onto whose root you have been grafted, you insult the people who have accepted you so that you might be converted from bad to good. You will not continue like that if you destroy the thing on which you stand.

"Boast not against the branches." He seems indeed to be comforting the Jew, but points out his vileness and extreme dishonor. And this is why he says not, "boast not," but, "boast not against" do not boast against them so as to sunder them. For it is into their place that ye have been set, and their goods that ye enjoy. Do you observe how he seems to be rebuking the one, while he is sharp upon the other? "But if thou boast," he says, "thou bearest not the root, but the root thee."

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 thou boast, thou bearest 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.

Do not rejoice in the fall of the Jews, or else you will hear that they do not abide through you but you through them and that you do not supply them with life, but they supply you.

Whenever I see a synagogue, the thought of the apostle always comes to me—that we should not boast against the olive tree whose branches have been broken off but rather fear. For if the natural branches have been cut off, how much more we who have been grafted on the wild olive should fear, lest we become like them.

Therefore, do not be arrogant and do not boast against the branches. What good is this to the branches that were broken off? For it is the root that supports. Do you see how he only praises the Jews in appearance, seeking merely to console them? However, even by this he spurs the Jews to zeal, showing the harm they have suffered and how others have received their possession and hold it.

Then when he says, but if you boast, he gives the reason for his admonition, saying: but if in spite of this admonition you boast by insulting the Jews, who stand upright or have been cut off, you should consider as a check to your boasting that you do not bear the root: but the root bears you, i.e., Judea did not receive salvation from the gentiles, but just the reverse: salvation is from the Jews (John 4:22). Hence, Abraham was promised that all the nations of the earth would be blessed in him (Gen 22:18).