John Chrysostom

"For Esaias," he says, "crieth concerning Israel." That is, speaks out boldly, and uses no dissimulation. Why then lay a charge against us, when they afore declared the same thing with more than trumpet's loudness? 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? …

Homily on Romans 16 ↗

Theophylact of Ohrid

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. …

Commentary on Romans ↗

Thomas Aquinas

Then, when he says Isaiah cried out, he proves his proposition with respect to the Jews and presents two texts from Isaiah. The first of these seems to pertain to all the Jews who came to believe; the second particularly to the apostles, at and Isaiah foretold. First, therefore, he says: we have indicated what Hosea said about the gentiles, but Isaiah cried out, i.e., clearly speaks about the conversion of Israel: cry, cease not, lift up your voice like a trumpet (Isa 58:1). …

Commentary on Romans ↗

Bonaventure

The fact that the Jews will be converted is certain because of Isaiah and the Apostle who teaches authoritatively: "Though the number of the children of Israel are as the sands of the sea, the remnant shall be saved." And again: "A partial blindness only has befallen Israel, until the full number of the Gentiles should enter." The Jews oppose to the fact that none of the prophesied peace has come about as yet. …

Collations on the Hexaemeron, Collation 15 ↗