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)