Romans 9:25

Having explained the promise, and proved the divine sovereignty, the apostle here shows how the rejection of the Jews, and the taking in of the Gentiles, were foretold in the Old Testament, and therefore must needs be very well consistent with the promise made to the fathers under the Old Testament. It tends very much to the clearing of a truth to observe how the scripture is fulfilled in it. The Jews would, no doubt, willingly refer it to the Old Testament, the scriptures of which were committed to them. Now he shows how this, which was so uneasy to them, was there spoken of. I. By the prophet Hosea, who speaks of the taking in of a great many of the Gentiles, Hos 2:23 and Hos 1:10. The Gentiles had not been the people of God, not owning him, nor being owned by him in that relation: "But," says he, "I will call them my people, make them such and own them as such, notwithstanding all their unworthiness." A blessed change! Former badness is no bar to God's present grace and mercy. - And her beloved which was not beloved. Those whom God calls his people he calls beloved: he loves those that are his own. And lest it might be supposed that they should become God's people only by being proselyted to the Jewish religion, and made members of that nation, he adds, from Hos 1:10, In the place where it was said, etc.

— Matthew Henry's Concise Commentary (public domain)

As he saith also in Osee--"Hosea." I will call them my people, which were not my people; and her beloved, which was not beloved--quoted, though not quite to the letter, from Hos 2:23, a passage relating immediately, not to the heathen, but to the kingdom of the ten tribes; but since they had sunk to the level of the heathen, who were "not God's people," and in that sense "not beloved," the apostle legitimately applies it to the heathen, as "aliens from the commonwealth of Israel and strangers to the covenants of promise" (so Pe1 2:10).

— Jamieson-Fausset-Brown Commentary (public domain)