11 “Blessed is the man whom You chasten, O Lord: and teachest him from Your law”. Behold, you have the counsel of God, wherefore He spares the wicked: the pit is being dug for the sinner. You wish to bury him at once: the pit is as yet being dug for him: do not be in haste to bury him. What mean the words, “until the pit be dug up for the sinner”? Or whom does He mean by sinner? One man? No. Whom then? The whole race of such that are sinners? No; them that are proud; for he had said before, “Reward the proud after their deserving.”
For that publican, who would not so much as lift up his eyes to heaven, but “smote upon his breast, saying, God be merciful to me a sinner,” was a sinner; but since he was not proud, and since God will render a recompense to the proud; the pit is being dug not for him, but for them that are such, until He render a recompense to the proud. In the words then, “until the pit be dug up for the ungodly,” understand the proud. Who is the proud? He who does not by confession of his sins do penance, that he may be healed through his humility.
Who is the proud? He who chooses to arrogate to himself those few good things which he seems to possess, and who does detract from the mercy of God. Who is the proud? He who although he does ascribe unto God his good works, yet insults those who do not those good works, and raises himself above them....This then is the Christian doctrine: no man does anything well except by His grace. A man's bad acts are his own: his good he does of God's bounty. When he has begun to do well, let not him ascribe it unto himself: when he has not attributed it to himself, let him give thanks to Him from whom he has received it. But when he does well, let him not insult him who does not as he does nor exalt himself above him: for the grace of God is not stayed at him, so that it cannot reach another.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)