Thomas Aquinas, on Ps 50:3

“Have mercy on me, O God, according to thy great mercy. And according to the multitude of thy tender mercies blot out my iniquity.”

“"Because." Here he confesses his guilt. And first, he confesses the guilt. Second, he shows this confession to be acceptable to God. First, therefore, he confesses the guilt. Second, he aggravates the guilt, at "against you alone have I sinned." Third, he demonstrates its origin, at "behold indeed." He therefore recognizes his guilt, saying, "because my iniquity." Some do not recognize their sins for three reasons: because reason is weighed down by the gravity of sin. Prov. 18: "When the wicked man comes to the depth of sins, he scorns." Ps. 39: "My iniquities have overtaken me, and I was not able to see." Also, because they do not remember. Eccl. 5: "He has forgotten his delights." Also, because of the flattery of men. Ps. 9: "The sinner is praised in the desires of his soul." And therefore, because others praise him for his sins, he himself does not recognize them. But happy is he who recognizes his sin, as David did. Prov. 14: "The heart knows the bitterness of its soul; in its joy no stranger shall intermeddle." As to the second, he says, "and my sin is always before me." Some are those who, even if they recognize their sin, nevertheless do not detest it; but this man always has his sin before him as something contrary, harmful, and detestable. And he says "always." Some are those who detest sin for a time. Jas. 1: "He beheld himself and went away," etc. Is. 38: "I will recount to you all my years," etc. "My iniquity I know." Another text: "before me"; and thus it designates that he recognizes his guilt and that he continually meditates upon it. And this was established before God through Nathan the prophet, under the likeness.”

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