Romans 9:24

Even us whom he also called, not from the Jews only, but also from the Gentiles? As he saith also in Hosea, I will call that my people, which was not my people; And her beloved that was not beloved.

Romans 9:24 concludes the long question that began back in Romans 9:22 with the words "What if ..." The import of this long interrogation is "Who should think it extraordinary, or something to wonder about, that God would at last reject that nation which had so long been rejecting him?" Paul at this point proceeded to show, by the quotation of a number of prophecies, that just these very things, the calling of the Gentiles and the rejection of Israel had been exactly foretold by God's prophets.

The verse quoted here is from Hosea 2:23 and can be understood in no other way except as a promise that Gentiles will finally become God's people.