This is a difficult passage in the King James translation so I will paraphrase it, taking from other translations on occasion.
Concerning the Gentiles, God says in Hosea that those who were not My people, I will now call my people. And I will love those I didn’t love before. At one time they were told, "You are not My people." But now God will say, "You are children of the living God."
Concerning Israel, Isaiah wrote, "Although the people of Israel are as numerous as the sand on the seashore, only a small number will be saved because the Lord will carry out his sentence on the earth quickly and with finality." It will be just as Isaiah said previously:
"Unless the Lord Almighty had left us some descendants, we would have become like Sodom and Gomorrah."
Paul quotes from Isaiah that it is only by God's free grace that even a remnant out of Israel will be saved. It’s not because they deserved it, but because God ordered and willed it.
Hosea prophesied God would save a people, namely the Gentiles, “who were not a people.” They were strangers to the covenants, aliens to the commonwealth of Israel, without hope, and yet, through God's sovereign grace, He called a people His people who were not His people because they put heir faith in Him. Hosea's prophecy is being fulfilled today in this wonderful day of grace.
Paul asks another question in verses 30-33: "What shall we say then? That the Gentiles, which followed not after righteousness, have attained to righteousness, even the righteousness which is of faith. But Israel, which followed after the law of righteousness, hath not attained to the law of righteousness. Wherefore? Because they sought it not by faith, but as it were by the works of the law. For they stumbled at that stumb