1 As we listened with much attention, while the Psalm was in reading, so let us listen attentively, while the Lord reveals the mysteries which He has deigned to obscure in this passage. For some mysteries in the Scriptures are shut up for this reason, not that they may be denied, but that they may be opened unto those who knock. If therefore ye knock with affection of piety, and sincere heartfelt love, He, who sees from what motives ye knock, will open unto you. It is known unto all of us (and I wish we may not be among their number), that may murmur against God's long-suffering, and grieve either that impious and wicked men live in this world, or that they have great power; and what is more, that the bad generally have great power against the good, and that the bad often oppress the good; that the wicked exult, while the good suffer; the evil are proud, while the good are humbled.
Observing such things in the human race (for they abound), impatient and weak minds are perverted, as if they were good in vain; since God averts, or seems to avert, His eyes from the good works of the pious and faithful, and to promote the wicked in those pleasures which they love. Weak men, therefore, imagining that they live well in vain, are induced either to imitate the wickedness of those whom they see flourishing: or if either through bodily or mental weakness they are deterred from doing wrong by a fear of the penal laws of the world; not because they love justice, but, to speak more openly, fearing the condemnation of men among men, they refrain indeed from wicked deeds, but refrain not from wicked thoughts.
And among their wicked thoughts, the chief is the wickedness which leads them impiously to imagine that God is neglectful, and regardless of human affairs: and that He either holds in equal estimation the good and the wicked: or even, and this is a still more pernicious notion, that He persecutes the good, and favours the wicked. He who thinks thus, although he does no harm to any man, does the greatest to himself, and is impious against himself, and by his wickedness hurts not God, but slays himself....
Source: The Enarrations, or Expositions, on the Psalms (New Advent)