John Chrysostom

And he seems to be bringing a testimony beside his purpose. For it does not say, Blessed are they whose faith is reckoned for righteousness. But he does so on purpose, not through inadvertency, to show the greater superiority. For if he be blessed that by grace received forgiveness, much more is he that is made just, and that exhibits faith. For where blessedness is, there all shame is removed, and there is much glory, since blessedness is a greater degree both of reward and of glory. …

Homily on Romans VIII ↗

Theophylact of Ohrid

For if he who receives forgiveness by grace is blessed, then far more blessed is he who has shown faith and been justified by it. Why, he says, do you hesitate over the fact that he receives forgiveness of sins by grace? You see that he who has received remission by grace is called blessed; for the prophet would not have called him blessed if he did not know that he possesses great glory: for blessedness is something exceedingly important and higher than righteousness itself; it is the summit of all the good things we receive from …

Commentary on Romans ↗

Thomas Aquinas

Then when he says, blessed are they, he presents David's words containing the previous judgment and says that those whose sins are forgiven are blessed; consequently, they did not previously have good works, from which they obtained justice or happiness. But sin is divided into three classes: original, actual mortal, and actual venial. First, in regard to original sin he says: blessed are they whose iniquities are forgiven. …

Commentary on Romans ↗