Thomas Aquinas, on Ps 13:1

“Unto the end, a psalm for David. The fool hath said in his heart: There is no God, They are corrupt, and are become abominable in their ways: there is none that doth good, no not one.”

“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. First he proposes the root of their malice. Second the progress of their malice: "They are corrupt," etc. As it is said in Sir. 10: "The beginning of all sin is pride, and the beginning of man's pride is to fall away from God." That a man, therefore, does not have God in his heart is the principle of malice; and therefore he says, "The fool has said in his heart, there is no God": Wis. 1: "Wisdom will not enter into a malicious soul, nor dwell in a body subject to sins." But can he say this? To say in one's heart is to think. But can one think that God does not exist? Anselm says that no one can. Likewise Damascene. The knowledge of God is naturally implanted in all: no one can think that what is naturally known does not exist. But it should be known that we can speak about the knowledge of God in two ways: namely, according to himself, or as regards us. If in the first way, then without doubt it cannot be thought that he does not exist: for no proposition can by its nature be thought false whose predicate is included in the definition of the subject. It should be noted, however, that existence in God is different from existence in other things, because the existence of God is his substance. Therefore, whoever speaks of God according to himself, speaks of his existence; and therefore according to himself it cannot be thought that he does not exist. And the statement of Damascene is resolved: because what is naturally implanted is known indeterminately, namely that God exists, but not what God is; but this is held through faith. "God" is said from "Theos," which means "to burn away all malice." Therefore someone says that God does not exist when he thinks that he is not omnipotent, and that he does not have care of human affairs: Job 21: "Who is the Almighty, that we should serve him?" This can be referred to the Jews who said that Christ was a mere man, not God. Jn. 10: "You, being a man, make yourself God." These Jews, not believing in him who was promised in the law, say "there is no God" -- this one, namely, who preaches to us. And the fool said this, because they were unwilling to receive the wisdom of God, having the eyes of their mind blinded; Ps. 81: "They have not known, nor have they understood." Wis. 2: "For their own malice has blinded them." Or here the sinner is rebuked. First for the sin of the heart in consent, at "The fool has said." Second for the sin of action, at "They are corrupt." Third for the sin of habit, at "And they have become abominable." First he calls the sinner a fool; because he does not have wisdom, so that he says, etc. Likewise, because spiritual things have no savor for him; 1 Cor. 2: "The natural man does not perceive the things of God." Consequently, the progress of malice is set forth: "They are corrupt and have become abominable." Just as the two parts of justice are to do good and to avoid evil, so the two parts of injustice are to do evil and to avoid good. And first he sets forth the first part. Second, the second. Concerning the first, he sets forth two things. First, the perversity of vices. Second, their abomination. In bodies, corruption follows from the evaporation of natural heat expelled by an alien heat. For the natural heat of the soul is the love of God. When, therefore, the alien love of concupiscence and of other sins enters, God departs. And therefore, when he said "there is no God," he immediately adds "they are corrupt": Jer. 5: "They have denied God and said, It is not he," namely, the punisher of sinners, the rewarder of the just: Sir. 21: "The heart of the fool," namely of the sinner, "is like a broken vessel." They are corrupt, therefore -- sinners through evil action: Jn. 3: "Their works were evil" -- because after they lose gratuitous goods through consent, the natural goods in them are corrupted; and therefore punishment follows them: Ps. 96: "A fire shall go before him, and shall burn his enemies round about." Likewise, when a body putrefies, it becomes abominable. So the soul of a person, as long as the love of God is in it, is acceptable to God; but when it is corrupted through sin, it becomes abominable. What is abominable is that from which human appetite recoils: and therefore he says, "And they have become abominable," namely to God and men -- sinners through the habit of sinning: Jer. 2: "How exceedingly base have you become, repeating your ways." Hos. 9: "They were alienated in confusion, and became abominable like the things they loved." And he said "in their pursuits," because through these they arrive at abominable things. Or they do so studiously, according to Jerome. For God finds more abominable the studied willingness to sin than the sin itself: Job 34: "They have deliberately turned away from him, and would not understand any of his ways." Another reading has: "They have corrupted and made abominable their pursuit," namely of wisdom and discipline: Prov. 1: "They have held discipline hateful, and have not received the fear of the Lord": Ez. 8: "You shall see yet greater abominations." Consequently he treats of the avoidance of good. "There is none who does good," because "there is no just man on earth who does good and does not sin" (Eccl. 7). "Not even one," that is, except Christ, because he alone had neither contracted sin nor committed sin. The Blessed Virgin had contracted sin: Eccl. 7: "One man among a thousand I have found; a woman among all these I have not found." Or "not even one," because not even one person perfectly does good. This is true, given that they have said "there is no God," and "they are corrupt."”

Imported from an open dataset — not yet checked against the printed edition.