Thomas Aquinas, on Ps 39:12

“Withhold not thou, O Lord, thy tender mercies from me: thy mercy and thy truth have always upheld me.”

“Another cause is the necessity of evils. And he presents a twofold evil: namely evils inflicted from without, and evils from within, at "My iniquities have overtaken me." As to the first he says, "For evils without number have surrounded me," namely evils that are inflicted upon me both by the world and by enemies: Ps. 117: "They surrounded me like bees"; and he says, "without number," because there are infinite dangers in the world and infinite wicked people: Eccl. 1: "The number of fools is infinite." The interior evils are sins; and these evils are dangerous in two ways: because of their gravity, since "my iniquities have overtaken me," that is, my sins have bound me by their weight: Prov. 5: "His own iniquities capture the wicked man"; "and I was not able to see": Wis. 2: "Their own malice has blinded them": Is. 59: "Your iniquities have made a division between you and your God." Likewise, they are dangerous because of their multitude. Hence he says, "They have been multiplied beyond the hairs of my head." For just as hairs are innumerable, so sins are innumerable, and especially venial sins: which, if they do not terrify because of their weight, nevertheless terrify because of their multitude. The Gloss says: if you have avoided grave sins, beware lest you be overwhelmed by sand; not that venial sins of whatever kind and however many constitute a mortal sin, but because they dispose toward it: Jas. 3: "In many things we all offend." The effect of this is the distraction of the heart: Eccl. 10: "Dying flies spoil the sweetness of the ointment." And therefore he says, "And my heart has forsaken me"; as if to say, even if they do not take away charity, they nevertheless impede fervor, and so the heart is distracted so that it is not fervent: 2 Sam. 7: "Your servant has found his heart to pray this prayer to you." Or, "My heart has forsaken me," that is, it has not thought about what is useful for me: Ps. 37: "The light of my eyes is not with me."”

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