Augustine of Hippo

"The fool has said in his heart, There is no God" [Psalm 14:1]. For not even have certain sacrilegious and abominable philosophers, who entertain perverse and false notions of God, dared to say, "There is no God." Therefore it is, has said "in his heart;" for that no one dares to say it, even if he has dared to think it. …

Exposition on Psalm 14 ↗

Thomas Aquinas

Above, the Psalmist reproached the deceitfulness of his enemies; here he sets forth their malice. The title is: "Unto the end, a Psalm of David." And concerning this he does two things. First he manifests their malice. Second he sets forth the hope of his liberation from them, at "Shall they not know," etc. And concerning the first he does two things. First he proposes their malice. Second he certifies that this malice is in them, at "The Lord from heaven," etc. The first is divided into two. …

Exposition on the Psalms of David ↗

Bonaventure

The Psalm says: The fool has said in his heart: there is no God; but to say in the heart is to think: therefore that God does not exist can be thought, at least by the fool. To that which is objected to the contrary from the Psalm and from Damascene, the response is already clear: because it proceeds from doubt which comes from a deficiency of reason, of the kind that exists in the foolish intellect, which, darkened by its own dimness, neither sufficiently resolves nor rightly compares nor fully apprehends the meaning of this name …

Disputed Questions on the Mystery of the Trinity, Question 1 ↗