In the place from which these words are taken, the prophet Isaiah calls heaven and earth as witnesses. He denounces the people of Israel for impiety, then depicts the miserable condition into which they fell because of this impiety.
“Your land is desolate, your cities are burned with fire. Strangers devour your country before you, and it is desolate, as overthrown by strangers” (cf. Is 1:7). Jerusalem alone remained, like a booth in a vineyard.
This is very similar to what happened under Hezekiah, when God wondrously saved Jerusalem from the Assyrians.
After this, the Prophet adds that if God had not left us a seed, all of us to the last man would have been destroyed. It would have happened as it did with Sodom and Gomorrah.
This seed left among us saved us. For its sake the Lord God spared the rest of us also.
Consequently, not all who remained alive are the saving seed. This seed is among them, and for its sake all who escaped final destruction were spared.
What then is this seed? It is the company of persons opposite to those who drew down the heavenly punishment. Those rejected God, while these, it follows, remain faithful to Him.
Those were filled with sins, while these, therefore, keep God’s commandments and advance in every virtue. Those angered the Holy One of Israel in this way, while these are clearly pleasing to Him (see Is 1:2-4).
Therefore God preserved them whole, and for their sake many others. Thus the seed in the Prophet here means people who believe in God, fear Him, and live holily according to His commandments.
If we bring this concept into what was said earlier, “the remnant shall be saved,” we receive this thought. The prophet Isaiah already foresaw that from the great multitude of the Jews then living, very few would be saved.
These were precisely those who fear God and love to keep His commandments. Such are all who leave Judaism and become Christians. They are the remnant of whom it was foretold that they would be saved.
It seems that, in citing this passage about the seed that was left, the Apostle intended nothing other than to explain what this remnant is which will be saved, as was said above.
But its meaning may also be somewhat broadened. For the sake of this saved remnant, for the sake of this preserved seed, all the other Jews were also left to live, from the beginning until now.
Because of their God-fighting, impiety, and lawlessness, the Jews ought long ago to have been destroyed, like the people of Sodom and Gomorrah.
Other nations also acted impiously and lawlessly. But they did not know the true God and had not heard His Law. These, however, knew the true God.
He had made Himself known to them many times in the most tangible way, and they had heard the Law from His own mouth. Therefore they were inexcusable when they acted impiously and lawlessly.
For this they ought long ago to have been destroyed. If they were not destroyed, it was only because among them God always preserved a seed worthy of His mercy.
For its sake He spared the whole mass of the people as well. This seed, properly speaking, must be reckoned as the seed of Abraham, to which alone the promise belongs.
This seed is especially precious in God’s eyes because from it was to come that one Seed, in whom all nations would be blessed. This Seed was mentioned already in Paradise before the expulsion from it, and then was continually remembered.
That seed, always guarded by God, foresaw this one Seed who was to be born from it. It was one with Him in spirit.
By this union it nourished its fear of God and righteousness, and always remained in God’s good pleasure. At last that Seed was born, accomplished His work in His own person, and sent His friends to gather to Him all who had lived in expectation of Him.
This is what is now being done, the Apostle could say. The apostolic preaching gathers them. If it does not take all, this is because not all are of this race.
Through us the Lord takes to Himself those who are His. Those who had previously been His, He Himself took when He descended into Hades.
Therefore, Jews, you have no reason to marvel or be perplexed when you see that not all come to the faith. Nothing extraordinary is happening here.
Only what the Prophets long ago foretold is being fulfilled, concerning the saved remnant and the preserved seed.
Here the Apostle ends his proof that the promise has not fallen away. This remains true although not all Jews come into the enclosure of faith, and through it into the inheritance of the spiritual blessings promised to the fathers.
It also remains true although, while the Jews remain outside the inheritance, the Gentiles enter into the inheritance in their place.
Throughout the whole course of the proof, the Apostle only hinted that if this is so, it is because some prove worthy and others unworthy. Now he says this openly, showing wherein the worthiness of some and the unworthiness of others consist.