John Chrysostom

You see that it is not the Law only that faith establisheth, but the promise of God also that it will not allow to fall to the ground. But the Law, on the other hand, by being kept to unseasonably, makes even the faith of none effect, and hindereth the promise. By this he shows that faith, so far from being superfluous, is even necessary to that degree, that without it there is no being saved. For the Law worketh wrath, as all have transgressed it. …

Homily on Romans VIII ↗

Theophylact of Ohrid

Since the law produces wrath, it is said that Abraham was justified and became an heir by faith, so that everything would be by grace. And why is grace necessary? "So that the promise would be firm." For grace, unlike the law, has no transgression, so that what is given would not be uncertain. …

Commentary on Romans ↗

Thomas Aquinas

After showing that the promise made to Abraham and his seed was not to be fulfilled through the law, the Apostle now shows that it is to be fulfilled through faith. In regard to this he does three things: first, he shows through what such a promise is to be fulfilled; second, in whom it is to be fulfilled, at to all the seed; third, by whom it is to be fulfilled, at who quickens the dead. First, therefore, he concludes to his proposition, as it were by division. …

Commentary on Romans ↗