Augustine of Hippo

In fact, Solomon gives over the entire book of Ecclesiastes to suggesting, with such fullness as he judged adequate, the emptiness of this life, with the ultimate objective, to be sure, of making us yearn for another kind of life which is no unsubstantial shadow under the sun but substantial reality under the sun's Creator. For a person becomes as insubstantial as the insubstantiality that surrounds him, and it is by God's righteous decree that he, too, must pass away like a shadow.

City of God 20.3 ↗

Jerome

"There is a futility that takes place on earth: sometimes there are righteous men who are treated as if they had done according to the deeds of the wicked; and there are wicked men who are treated as if they had done the deeds of the righteous. I declared, this, too, is vanity. …

Commentary on Ecclesiastes ↗

Gregory the Dialogist

So Solomon bears witness, saying, "There are just men to whom many things happen, as though they had done the deeds of the wicked; and there are wicked, who are as secure as though they had the deeds of the just." God no doubt so ordains it of his inestimable mercy, that scourges should torture the just, lest their doings should elate them, and that the unjust should pass this life at least without punishment, because, by their evil doings, they are hastening onward to those torments that are without end. …

Morals on the Book of Job, Book 24, Section 44 ↗