Isa 10:21

“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. Serve your brother, therefore: but then you will feel the benefit of servitude when you begin to obey your brother willingly, rather than forcibly.”

“Do you also see that he does not say that all will be saved but only those who are worthy will be saved?… He does not speak of the "sands of the sea" without cause, but he does so to remind them of the ancient promise they had made themselves unworthy of. Why are you bothered, as though the promise has not been kept? The prophets demonstrate that not everyone will be saved.… It not only demonstrates that only a few will be saved, and not everyone, but also says how they will be saved. How are they to be saved, and by what manner will God consider them to be worthy?… Faith is such that it holds salvation in a few short words.”

“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.”

“שאר יעקב. The remnant shall return. This is the name of the prophet’s son, which is to be explained now. Supply יעקב, after the first שאר. The remnant of Jacob, that is Judah, will return; repeat likewise ישוב before אל: The remnant of Jacob will return to the mighty God (comp. Prov. 21:14). The verse, if written in full, would run thus: שאר יעקב ישוב אל אל גבור שאר יעקב ישוב,. The remnant of Jacob will return, the remnant of Jacob will return to the mighty God. Mighty, who is able to help them.”

“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; and as to the converted, the remnant of Jacob, who were left by the Assyrians: save, O Lord, your people, the remnant of Israel (Jer 31:7).”