Bede

The foolishness of a man supplanteth his steps, etc. It is the habit of fools, that when they abandon the way of truth through sinning, they do not admit they have erred, but refer the origin of guilt to their Creator, as if He has given the opportunity for sinning, either because He made man fragile, or because He allowed a crafty enemy to tempt him. Hence also the first parent of our race, after the excess of transgression, being reproved by the Lord, instantly fled to the defense of an excuse, saying: The woman whom You gave to be with me, she gave me of the tree, and I ate (Gen. III). And the woman said: The serpent deceived me (Ibid.). For they indeed turned against the Creator what they had sinned: he, that he had received a woman from the Lord as a companion through whom he perished; she, that the Lord had placed the serpent who deceived her in paradise. Against this the Wise Man prays to the Lord not to incline his heart to an evil word, to excuse excuses in sins. But also, he, failing his steps against God, burns with fervor in his mind, who, despising divine commands through his own inertia, even reproaches God Himself with an insane mind, as if He had imposed unbearable burdens on men.

"As the roaring of a lion, so is the anger of a king," etc. It speaks of God the King, who in judgment is both cheerful and gentle to the just, but will appear terrible to the unjust. "A foolish son is a father's grief." God, who is always impassible and placid in His nature, is nevertheless said to grieve in our manner when He sees that men, whom He created to believe in and praise Him, rather serve a malignant enemy than Himself. Hence Moses also says of Him, "He repented that He had made man on earth." And being inwardly touched with sorrow of heart, He said, "I will destroy man whom I have created from the face of the earth" (Gen 6:7). "And a contentious woman is like a continuous dripping." Just as roofs that continuously drip indeed receive rain from heaven, yet do not distribute it for any useful purpose, but rather cause annoyance to those living below; so too, indeed, the Church of heretics, improperly interpreting and arguing against Catholics, receives gifts of heavenly words, not for the salvation of souls, but for the misuse of its wickedness. For dripping roofs indeed receive pure drops of rain, but render those beneath them filthy, and a heretic, though he hears the purest words of the heavenly oracle with his body, yet when he touches these with a defiled heart, he administers them mingled with filth to his audience. "Laziness induces sleep." He is called lazy, who, though correctly perceiving, is almost awake, yet is slothful by doing nothing. But laziness induces sleep, because even the vigilance of correct perception is lost for a while, whenever one ceases from the pursuit of good deeds. And rightly it is added: "And a loose soul shall hunger." For since it does not direct itself by striving towards higher things, it expands downward through neglect towards desires. And while it is not constrained by the vigor of diligent study, it is wounded by the craving for the lowest desires, so that by rejecting restraint through discipline, it scatters itself in hunger through the desires of pleasures.

Who can say, My heart is clean, I am pure from sin? It should be noted that He does not say, Who can have a clean heart and be pure from sin? But He says, Who can say, My heart is clean, I am pure from sin? Because there are those who, by the grace of God, can have according to human measure the purity of heart and work. Hence the Lord's saying, Blessed are the clean of heart, for they shall see God (Matthew 5); and in the psalm: Who shall ascend into the mountain of the Lord, or who shall stand in His holy place? He that has clean hands and a pure heart (Psalm 23). For if no one has a clean heart, and there is none pure from sin, it would certainly follow that no one would ascend the mountain of the Lord, nor would any man stand in His holy place. But because it is certain that many will ascend the mountain of the Lord, and will stand in His holy place, therefore many must have a clean heart, and according to the measure of human possibility, be pure from sin. Yet no one should rashly declare himself clean of heart and free from sin. For the boasting of one's own praise is foolish; it is rash to glory in one's own innocence or justice. And because there are those who tend to praise their own deeds as excellent and criticize the deeds of others as vile, it is rightly added:

Even by his pursuits, a youth is known, etc. For whomsoever you see striving for virtues, modesty, continence, listening to the wise, and observing the commandments of God, especially humility and simplicity, know that his works are pure and right. But whomsoever you find taking a contrary course, recognize him as a man of an impure and crooked heart, and either correct and chastise him or if you cannot, avoid and shun him, lest you yourself be corrupted by him. It should not seem contrary that here the diligent youth is testified to have pure and right works, but above he said: Who can say, My heart is clean, I am pure from sin? For in this verse, he advises diligence in living rightly; in that, he dissuades from presumption of one's purity; in this, he teaches that purity and rectitude should be held as much as possible in this life; in that, he warns that the subtlety of divine examination, by which the deeds and intentions of men are judged, should always be kept in mind. Therefore, the ancient interpreters also translated that place in this way: When the just king sits on the throne of judgment, who will boast of having a pure heart? Or who will boast of being clean from sin? They also rendered the verse we are explaining more clearly, saying: A young man who is with the just will have a straight path. He who walks with the wise will be wise. Conversely, a friend of fools will become like them.