Cyril of Alexandria

The holy Scripture often calls the church "the holy mountain" whose lesser part came from Israel. For if Israel had received the faith that is in our Lord Jesus Christ, they would have formed the greater part of the church's composition, and the multitude of the nations would have been added to them. But because they did not believe, they became the lesser of the two. The nations became greater, while Israel became quite small. For the remnant will be saved. …

Commentary On Isaiah 5:5.65:18-19 ↗

Jerome

And I will bring forth offspring from Jacob, and from Judah those who possess my mountains; my chosen ones will inherit it, and my servants will dwell there. They will pasture their flocks in the open fields and find rest in the valley of Achor, for my people who have sought me. He who above called the grape of the goblet, or the berry, or (as many wills) the cluster, now calls it the seed of Jacob and Judah, who possess the mountains or its mountain. …

Commentary on Isaiah ↗

Thomas Aquinas

Second, as to their advancement in good things. And first, as to the multiplication of their seed: and I will bring forth a seed out of Jacob, above: except the Lord of hosts had left us seed, we had been as Sodom (Isa 1:9). Second, as to the restoration of the inheritance of their fathers: and my elect shall inherit it: they shall possess you for their inheritance: and you shall be their inheritance (Ezek 36:12).

Commentary on Isaiah ↗