Romans 11:30

"According to the Gospel indeed they are enemies for your sake: but according to the election they are most dear for the sake of the fathers. For the gifts and the calling of God are without repentance. For as you also once did not believe God, but now have obtained mercy because of their unbelief: so these also have now not believed, that through the mercy shown to you they too may obtain mercy." The Apostle, still pursuing the same matters concerning Israel and the Gentiles, and reproaching the branches of the wild olive which insulted the broken branches of the olive tree, adds also these things: That Israel according to the Gospel has indeed been made an enemy to God, because it did not believe Christ: but so far as regards the honor due to the fathers, it is elect, and is held most dear with God. But election having once been granted to the seed of the fathers, and love conceded, God without doubt preserves his gifts and his calling toward the seed of those to whose merits he once bestowed this: nor does repentance come upon God, even if those upon whom the benefits promised to the fathers are conferred appear to be less worthy. But, as we have often advised, in the present passage also that distinction is to be observed, that the Israel which is an enemy to God is said to be that which cries out concerning Christ: "Away with him, away with him, crucify him." For how should they not be called enemies of God, who either then, or even now, have said such things, or say them? But when he says, "for your sake," this means, those namely whose salvation they envy, forbidding the apostles to speak to the Gentiles, and persecuting those who announce Christ. But according to the remnant which is said to be saved, in which the election of believers followed from Israel, they are "most dear for the sake of the fathers:" whose faith namely they follow, believing "in him who raised Christ Jesus from the dead." And according to this, toward such a seed "the gifts and the calling of God are without repentance." But after these things he opens also the hidden and deeper causes of their unbelief, and says: That just as you Gentiles once did not believe God, nor yet did God on that account utterly abandon you, but at last at some time you obtained mercy — yet the occasion of mercy being conferred upon you was the unbelief of the people of Israel — so also these who now from the people of Israel have not believed, and for their unbelief have been abandoned, so that the mercy of God might be turned toward you, will not be left forever in their unbelief; but after the dispensation of the fullness of the Gentiles has been fulfilled, they too shall obtain mercy.

"For as ye in times past have not believed God, yet have now obtained mercy through their unbelief; even so have these also now not believed, that through your mercy they may also obtain mercy. For God hath concluded them all in unbelief, that He might have mercy upon all."

He shows here that those of the Gentiles were called first. Then, as they would not come, the Jews were elected, and the same result occurred again. For when the Jews would not believe, again the Gentiles were brought over. And he does not stop here, nor does he draw the whole to a conclusion at their rejection, but at their having mercy shown them again. See how much he gives to those of the Gentiles, as much as he did to the Jews before. For when ye, he would say, "in times past did not obey," being of the Gentiles, then the Jews came in. Again, when these did not obey, ye have come. However, they will not perish forever. "For God hath concluded them all in unbelief," that is, hath convinced them, hath shown them disobedient; not that they may remain in disobedience, but that He may save the one by the captiousness of the other, these by those and those by these. Now consider; ye were disobedient, and they were saved. Again, they have been disobedient, and ye have been saved. Yet ye have not been so saved as to be put away again, as the Jews were, but so as to draw them over through jealousy while ye abide.

You did not believe when the Jews did, and now you have received mercy, but not because you have deserved it.

Paul shows that both Jews and Gentiles were guilty of the same thing and that they were likewise cleansed by one and the same grace.

You, he says, who were formerly called Gentiles, did not wish to obey: therefore the Jews were chosen and received the law. Again, when the Jews were called and did not obey Christ, you were chosen and shown mercy.

Then when he says, for as you also, he gives the reason for the future salvation of the Jews after their unbelief.
First, he shows a similarity between the salvation of both people;
second, the cause of this similarity, at for God has concluded.

First, therefore, he says: so I say that Israel will be saved, although they are now enemies. For as you also, gentiles, in times past did not believe God: you were once without God in the world (Eph 2:12); but now have obtained mercy: the gentiles are to glorify God for his mercy (Rom 15:9); I will have mercy on him who was without mercy (Hos 2:23). And this was through their unbelief, which was the occasion of your salvation, as was said above.