Cyril of Alexandria

This oracle has great force. For it does not simply say, "Light will be given to you by God," but it will be like lightning whose course and progress is sent by God, through which is clearly shown the desire of those who pray. By saying "first light," it instructs us that it will appear before time. For God, the guardian of all things, knew, as the giver of spiritual gifts, the time suited to each person for his blessings. …

Commentary On Isaiah 5:4.58:8 ↗

Jerome

Then your light shall break forth like the dawn, and your healing shall spring up quickly; your righteousness shall go before you, and the glory of the Lord shall be your rear guard. Then you shall call, and the Lord will answer; you shall cry for help, and he will say: Here I am. LXX: Then your light shall break forth like the morning; your healing shall spring forth speedily, and your righteousness shall go before you; the glory of God shall surround you. …

Commentary on Isaiah ↗

Thomas Aquinas

1028. Second, he shows the fruit of this counsel: then shall your light break forth. And first, as to the efficacy of their merits, then as to the works of their virtues: then shall your light break forth as the morning, namely, your merits will appear clearly in the rewards, about which you now complain to the Lord because they are not yet seen; the glory of the Lord shall gather you up, from captivity, or in the protection of his mercy: he will bring forth your justice as the light, and your judgment as the noonday (Ps 36:6).

Commentary on Isaiah ↗