Isaiah 10:21

And what does Isaiah cry? "Though the number of the children of Israel be as the sand of the sea, a remnant shall be saved." Do you see that he too does not say that all are to be saved, but that those that are worthy shall? For I regard not the multitude, he means, nor does a race diffused so far distress me, but those only do I save that yield themselves worthy of it. And he does not mention the "sand of the sea" without a reason, but to remind them of the ancient promise whereof they had made themselves unworthy. Why then are you troubled, as though the promise had failed, when all the Prophets show that it is not all that are to be saved? Then he mentions the mode of the salvation also. Observe the accuracy of the Prophet, and the judgment of the Apostle, what a testimony he has cited, how exceedingly apposite! For it not only shows us that those to be saved are some and not all, but also adds the way they are to be saved. How then are they to be saved, and how will God count them worthy of the benefit? "He will finish the work, and cut it short in righteousness," he says, "because a short work will the Lord make upon the earth." What he means then is somewhat of this sort. There is no need of fetching a circuit, and of trouble, and the vexation of the works of the Law, for the salvation is by a very short way. For such is faith, it holds salvation in a few short words.

This is therefore what the patriarch Isaac said: You will serve your brother. But when you have removed and freed yourself from his yoke on your neck, he is signifying two future peoples, one the son of a handmaid, the other of a free woman (for the letter is a servant, but grace is free), and that people who adheres to the letter will be a servant as long as they follow the interpreter of spiritual doctrine. Then also what the Apostle said will come to pass: That the remnants may be saved according to the choice of grace.

(Verse 20 onwards) And it shall come to pass in that day, that the remnant of Israel shall no more stay upon him that smote them, but shall stay upon the LORD, the Holy One of Israel, in truth. The remnant shall return, even the remnant of Jacob, unto the mighty God. For though thy people Israel be as the sand of the sea, yet a remnant of them shall return: the consumption decreed shall overflow with righteousness. For the Lord God of hosts will make a consummation and an abbreviation in the midst of all the land.

But yet grace from above sometimes looks upon these mighty men, and afflicts them by the very employments caused by their abundant goods, and intersperses with their prosperity, adverse, but profitable, tribulations: in order that, when sorrowful, they may turn to their heart, and learn how vainly they are engaged in perishable pursuits. Because the light of truth, which is concealed from proud and overbusied minds, is revealed to the afflicted and humbled. For light approaches, when the afflicted mind discerns the gloom of tribulation which it is enduring from perishable pursuits: for, if it had not some perception of the light within, it would not even see that it had lost the light. But this can be specially understood also of the Jews, who dared for this reason to speak against our Redeemer, coming in the flesh, because they were mighty in their own thoughts. But the light was hid from these mighty men; because, while they are persecuting in their pride the light of truth, they lost it. But because they are to be admitted to the faith at the end of the world, it is rightly subjoined, And ordereth it to return again. Whence also it is said by Isaiah, If the number of the children of Israel shall be as the sand of the sea, a remnant shall be saved. For the light then returns to them when they themselves return to confess the power of our Redeemer.

Second, as to their worship of idols, both as to manner, for in truth, the remnant, against what is said in 1 Kings 18:21: how long do you halt between two sides? If the Lord be God, follow him: but if Baal, then follow him; …