John Chrysostom

For reflect how great a thing it is to be persuaded and have full confidence that God is able on a sudden not to free a man who has lived in impiety from punishment only, but even to make him just, and to count him worthy of those immortal honors. Do not then suppose that this one is lowered in that it is not reckoned unto the former of grace. For this is the very thing that makes the believer glorious; the fact of his enjoying so great grace, of his displaying so great faith. And note too that the recompense is greater. …

Homily on Romans VIII ↗

Theophylact of Ohrid

The one who believes, although he does not work, nevertheless presents on his part faith — a thing of great significance; for to be convinced that God can not only free from punishment one who has lived in ungodliness, but also make him righteous, is a matter of high value. For this reason, "to the one who believes... his faith is counted as righteousness," that is, God accepts his faith — not in order to give him wages, but in order to justify him. Therefore the one who believes brings something on his part as well, namely faith.

Commentary on Romans ↗

Augustine of Hippo

The life of the soul is changeable. And when the soul lives in unrighteousness, that is its death; when again it becomes righteous, it becomes partaker of another life, which is not what itself is, inasmuch as by rising up to God, and cleaving to God, of Him it is justified. For it is said, "To him that believeth on Him that justifieth the ungodly, his faith is counted for righteousness." By forsaking God, it becomes unrighteous; by coming to Him, it is made righteous.

Tractates on John 19 ↗

Thomas Aquinas

Then when he says but to him, he shows how the eternal reward is related to faith, saying, but to him who works not outward works, for example, because he does not have time to work, as in the case of one who dies immediately after baptism, yet believes in him who justifies the ungodly, namely, in God, of whom he says below: God is he who justifies (Rom 8:33), his faith is reputed, i.e., faith alone without outward works, to justice, so that in virtue of it he is called just and receives the reward of justice, just as if he had done …

Commentary on Romans ↗