Rom. 9:26. And in the place where it was said to them: you are not My people, there they shall be called sons of the living God.
The Jews could say: you, Paul, are deceiving us by saying this. Therefore he brings forward Hosea, who cries out and says: "I will call those who were not My people, My people." Who then was "not His people"? The Gentiles. And who was "not beloved"? The Gentile Church. Yet the Gentiles became a people and beloved, and even, what is more important, sons of the living God. If someone should say that this was spoken about the Jews who had conducted themselves ungratefully but were afterwards received into grace, such an argument does not harm our explanation. For if this acceptance happened with them, what prevented it from happening with the Gentiles?
Rom. 9:27. Isaiah cries out concerning Israel: "Though the number of the sons of Israel be as the sand of the sea, only a remnant shall be saved."
He was not satisfied with pointing to Hosea, but brings Isaiah as a witness as well, who "proclaims," that is, boldly and fearlessly, that not all the Israelites will be saved, but those worthy of salvation (for this is what the remnant means, that is, the chosen), whom God left and set apart, that is, as worthy. By saying "as the sand of the sea," he reminds them of the Old Testament promise, of which they had made themselves unworthy. Therefore, do not be troubled, as though the promise has been broken. All the prophets foretell that not all are worthy of salvation.
Rom. 9:28. Completing and cutting short the word in righteousness, the Lord will make a decisive word upon the earth.
Now he shows how the remnant will be saved, and says that there is no need to labor, to go far, and to exhaust oneself with works of the law. God, he says, who brings to completion and accomplishes the word of faith in a short way throughout all the earth, will do this "in righteousness," that is, in order to justify those who have accepted it. "If you confess with your mouth Jesus as Lord, and believe in your heart that God raised Him from the dead, you will be saved" (Rom. 10:9). This is the shortened word, that is, the brief sayings of faith.
Rom. 9:29. And, as Isaiah foretold: if the Lord of Sabaoth had not left us a seed, we would have become like Sodom, and would have been made like Gomorrah.
Having said that the remnant will be saved, he now explains what this means, and says that God left us a chosen seed and bread, for the word "left" he used instead of "chose," so that if God had not preserved it, we would have been subjected to destruction, like the Sodomites and Gomorrahites, as those condemned for their sins.
Rom. 9:30. What then shall we say? That the Gentiles, who did not pursue righteousness, attained righteousness, the righteousness that is by faith.
Rom. 9:31. But Israel, which followed after the law of righteousness, hath not attained to the law of righteousness.
Here he gives the clearest resolution, showing why the Gentiles were accepted and the Israelites were rejected. The Gentiles, he says, holding to the righteousness of faith, were indeed justified, while the Israelites, ceaselessly seeking the "law of righteousness," that is, the law of works, did not attain to righteousness; because the law, which consisted of works, was not able to justify.
Rom. 9:32. Why? Because they sought it not by faith, but by the works of the law.
You ask: why did the Israelites not attain righteousness, even though they earnestly pursued it? Know that they sought justification not in faith, but as if in the works of the law.
Rom. 9:33. For they stumbled at the stumbling stone, as it is written: Behold, I lay in Zion a stumbling stone and a rock of offense; but everyone who believes in Him shall not be put to shame.
He stumbles who gazes at something extraneous and does not pay attention to what is under his feet. So too the Jews, gazing at the law, stumbled over Christ, that is, they did not believe. And Christ is called a stumbling stone and a rock of offense in relation to the end and disposition of those who did not believe. For in Himself He is laid as a foundation and support; because it is said: "he who believes in Him shall not be put to shame" (Isa. 28:16), whether Gentile or Jew, so that faith, not works, accomplishes and justifies all things.