2 “The unwise man has said in his heart, There is no God”. Such sort is it of men amid whom is pained and groans the Body of Christ. If such is this sort of men, of not many do we travail; as far as seems to occur to our thoughts, very few there are; and a difficult thing it is to meet with a man that says in his heart, “There is no God;” nevertheless, so few there are, that, fearing amid the many to say this, in their heart they say it, for that with mouth to say it they dare not.
Not much then is that which we are bid to endure, hardly is it found: uncommon is that sort of men that say in their heart, “There is no God.” But, if it be examined in another sense, is not that found to be in more men, which we supposed to be in men few and uncommon, and almost in none? Let them come forth into the midst that live evil lives, let us look into the doings of profligate, daring, and wicked men, of whom there is a great multitude; who foster day by day their sins, who, their acts having been changed into habit, have even lost sense of shame: this is so great a multitude of men, that the Body of Christ, set amid them, scarce dares to censure that which it is not constrained to commit, and deems it a great matter for itself that the integrity of innocence be preserved in not doing that which now, by habit, either it does not dare to blame, or if it shall have dared, there breaks out the censure and recrimination of them that live evil lives, more readily than the free voice of them that live good lives.
And those men are such as say in their heart, “There is no God.” Such men I am confuting. Whence confuting? That their doings please God, they judge. He does not therefore affirm, “some say,” but “The unwise man has said in his heart, There is no God.” Which men do so far believe there is a God, that the same God they judge with what they do to be pleased. But if you being wise dost perceive, how “the unwise man has said in his heart, There is no God,” if you give heed, if you understand, if you examine; he that thinks that evil doings please God, Him he does not think to be God.
For if God is, He is just; if He is just, injustice displeases Him, iniquity displeases. But you, when you think that iniquity pleases Him, dost deny God. For if God is one Whom iniquity displeases, but God seems not to you to be one whom iniquity displeases, and there is no God but one whom iniquity displeases, then when you say in your heart, God does countenance my iniquities, you say nothing else than, “There is no God.”
Source: The Enarrations, or Expositions, on the Psalms (New Advent)