1 Then follow these words: “The wicked plots against the just, and gnashes upon him with his teeth”: “But the Lord shall laugh at him”. At whom? Surely at the sinner, “gnashing upon” the other “with his teeth.” But wherefore shall the Lord “laugh at him”? “For He foresees that his day is coming.” He seems indeed full of wrath, while, ignorant of the morrow that is in store for him, he is threatening the just. But the Lord beholds and “foresees his day.” “What day?” That in which “He will render to every man according to his works.” For he is “treasuring up unto himself wrath against the day of wrath, and revelation of the just judgment of God.” But it is the Lord that foresees it; you do not foresee it. It has been revealed to you by Him who foresees it. You did not know of the “day of the unrighteous,” in which he is to suffer punishment. But He who knows it has revealed it to you. It is a main part of knowledge to join yourself to Him who has knowledge. He has the eyes of knowledge: have thou the eyes of a believing mind. That which God “sees,” be thou willing to believe. For the day of the unjust, which God foresees, will come. What day is that? The day for all vengeance! For it is necessary that vengeance should be taken upon the ungodly, that vengeance be taken upon the unjust, whether he turn, or whether he turn not. For if he shall turn from his ways, that very thing, that his “injustice has come to an end,” is the infliction of vengeance....
2. “The wicked have drawn out the sword, and have bent their bow, to cast down the poor and needy, and to slay such as be of upright heart”. “Their weapon shall enter into their own heart”. It is an easy thing for his weapon, that is, his sword, to reach your body, even as the sword of the persecutors reached the body of the Martyrs, but when the body had been smitten, “the heart” remained unhurt; but his heart who “drew out the sword against” the body of the just did not clearly remain unhurt. This is attested by this very Psalm. It says, Their weapon, that is, “Their sword shall,” not go into their body, but, “their weapon shall go into their own heart.” They would fain have slain him in the body. Let them die the death of the soul. For those whose bodies they sought to kill, the Lord has freed from anxiety, saying, “Fear not them who kill the body, but cannot kill the soul.”...
3. “And their bows shall be broken.” What is meant by, “And their bows shall be broken”? Their plots shall be frustrated. For above He had said, “The wicked have drawn out the sword and bent their bows.” By the “drawing out of the sword” he would have understood open hostility; but by the“bending of the bow,” secret conspiracies. See! His sword destroys himself, and his laying of snares is frustrated. What is meant by frustrated? That it does no mischief to the righteous. How then, for instance (you ask), did it do no mischief to the man, whom it thus stripped of his goods, whom it reduced to straitened circumstances by taking away his possessions? He has still cause to sing, “A little that a righteous man has, is better than great riches of the ungodly”.
4....“For the arms of the wicked shall be broken”. Now by “their arms” is meant their power. What will he do in hell? Will it be what the rich man had to do, he who was wont “to fare sumptuously” in the upper world, and in hell “was tormented”? Therefore their arms shall be broken; “but the Lord upholds the righteous.” How does He “uphold” them? What says He unto them? Even what is said in another Psalm, “Wait on the Lord, be of good courage; and let your heart be strengthened. Wait, I say, on the Lord.” What is meant by this, “Wait on the Lord”? Thou sufferest but for a time; you shall rest for ever: your trouble is short; your happiness is to be everlasting. It is but for “a little while” you are to sorrow; your joy shall have no end. But in the midst of trouble does your “foot” begin to “slip”? The example even of Christ's sufferings is set before you. Consider what He endured for you, in whom no cause was found why He should endure it? How great soever be your sufferings, you will not come to those insults, those scourgings, to that robe of shame, to that crown of thorns, and last of all to that Cross, which He endured; because that is now removed from the number of human punishments. For though under the ancients criminals were crucified, in the present day no one is crucified. It was honoured, and it came to an end. It came to an end as a punishment; it is continued in glory. It has removed from the place of execution to the foreheads of Emperors. He who has invested His very sufferings with such honour, what does He reserve for His faithful servants?...
Source: The Enarrations, or Expositions, on the Psalms (New Advent)