3 And that it might be clear that the already perfect soul, which is to be on her guard against the most insidious snares of the devil only, says this, see what follows. “O Lord my God, if I have done this”. What is it that he calls “this”? Since he does not mention the sin by name, are we to understand sin generally? If this sense displease us, we may take that to be meant which follows: as if we had asked, what is this that you say, “this”? He answers, “If there be iniquity in my hands.” Now then it is clear that it is said of all sin, “If I have repaid them that recompense me evil”. Which none can say with truth, but the perfect. For so the Lord says, “Be perfect, as your Father which is in heaven; who makes His sun to rise upon the good and the evil, and rains on the just and the unjust.” He then who repays not them that recompense evil, is perfect. When therefore the perfect soul prays “for the words of Chusi, the son of Jemini,” that is, for the knowledge of that secret and silence, which the Lord, favourable to us and merciful, wrought for our salvation, so as to endure, and with all patience bear, the guiles of this betrayer: as if He should say to this perfect soul, explaining the design of this secret, For you ungodly and a sinner, that your iniquities might be washed away by My blood-shedding, in great silence and great patience I bore with My betrayer; will you not imitate me, that you too may not repay evil for evil? Considering then, and understanding what the Lord has done for him, and by His example going on to perfection, the Psalmist says, “If I have repaid them that recompense me evil:” that is, if I have not done what You have taught me by Your example: “may I therefore fall by mine enemies empty.” And he says well, not, If I have repaid them that do me evil; but, who “recompense.” For who so recompenses, had received somewhat already. Now it is an instance of greater patience, not even to repay him evil, who after receiving benefits returns evil for good, than if without receiving any previous benefit he had had a mind to injure. If therefore he says, “I have repaid them that recompense me evil:” that is, If I have not imitated You in that silence, that is, in Your patience, which You have wrought for me, “may I fall by mine enemies empty.” For he is an empty boaster, who, being himself a man, desires to avenge himself on a man; and while he openly seeks to overcome a man, is secretly himself overcome by the devil, rendered empty by vain and proud joy, because he could not, as it were, be conquered. The Psalmist knows then where a greater victory may be obtained, and where “the Father which sees in secret will reward.” Lest then he repay them that recompense evil, he overcomes his anger rather than another man, being instructed too by those writings, wherein it is written, “Better is he that overcomes his anger, than he that takes a city.” “If I have repaid them that recompense me evil, may I therefore fall by my enemies empty.” He seems to swear by way of execration, which is the heaviest kind of oath, as when one says, If I have done so and so, may I suffer so and so. But swearing in a swearer's mouth is one thing, in a prophet's meaning another. For here he mentions what will really befall men who repay them that recompense evil; not what, as by an oath, he would imprecate on himself or any other.
4. “Let the enemy” therefore “persecute my soul and take it”. By again naming the enemy in the singular number, he more and more clearly points out him whom he spoke of above as a lion. For he persecutes the soul, and if he has deceived it, will take it. For the limit of men's rage is the destruction of the body; but the soul, after this visible death, they cannot keep in their power: whereas whatever souls the devil shall have taken by his persecutions, he will keep. “And let him tread my life upon the earth:” that is, by treading let him make my life earth, that is to say, his food. For he is not only called a lion, but a serpent too, to whom it was said, “Earth shall you eat.” And to the sinner was it said, “Earth you are, and into earth shall you go.” “And let him bring down my glory to the dust.” This is that dust which “the wind casts forth from the face of the earth,” to wit, vain and silly boasting of the proud, puffed up, not of solid weight, as a cloud of dust carried away by the wind. Justly then has he here spoken of the glory, which he would not have brought down to dust. For he would have it solidly established in conscience before God, where there is no boasting. “He that glories,” says the Apostle, “let him glory in the Lord.” This solidity is brought down to the dust if one through pride despising the secrecy of conscience, where God only proves a man, desires to glory before men. Hence comes what the Psalmist elsewhere says, “God shall bruise the bones of them that please men.” Now he that has well learned or experienced the steps in overcoming vices, knows that this vice of empty glory is either alone, or more than all, to be shunned by the perfect. For that by which the soul first fell, she overcomes the last. “For the beginning of all sin is pride:” and again, “The beginning of man's pride is to depart from God.”
5. “Arise, O Lord, in Your anger”. Why yet does he, who we say is perfect, incite God to anger? Must we not see, whether he rather be not perfect, who, when he was being stoned, said, “O Lord, lay not this sin to their charge”? Or does the Psalmist pray thus not against men, but against the devil and his angels, whose possession sinners and the ungodly are? He then does not pray against him in wrath, but in mercy, whosoever prays that that possession may be taken from him by that Lord “who justifies the ungodly.” For when the ungodly is justified, from ungodly he is made just, and from being the possession of the devil he passes into the temple of God. And since it is a punishment that a possession, in which one longs to have rule, should be taken away from him: this punishment, that he should cease to possess those whom he now possesses, the Psalmist calls the anger of God against the devil. “Arise, O Lord; in Your anger.” “Arise” (he has used it as “appear”), in words, that is, human and obscure; as though God sleeps, when He is unrecognised and hidden in His secret workings. “Be exalted in the borders of mine enemies.” He means by borders the possession itself, in which he wishes that God should be exalted, that is, be honoured and glorified, rather than the devil, while the ungodly are justified and praise God. “And arise, O Lord my God, in the commandment that You have given:” that is, since You have enjoined humility, appear in humility; and first fulfil what You have enjoined; that men by Your example overcoming pride may not be possessed of the devil, who against Your commandments advised to pride, saying, “Eat, and your eyes shall be opened, and you shall be as gods.”
Source: The Enarrations, or Expositions, on the Psalms (New Advent)