9 But that which he adds, “Pour forth Your anger upon the nations which have not known You, and upon the kingdoms which have not called upon Your name”; this too is a prophecy, not a wish. Not in the imprecation of malevolence are these words spoken, but foreseen by the Spirit they are predicted: just as in the case of Judas the traitor, the evil things which were to befall him have been so prophesied as if they were wished. For in like manner as the prophet does not command Christ, though in the imperative mood he gives utterance to what he says, “Gird Your sword about Your thigh, O Most Mighty: in Your beauty and in Your goodliness, both go on, and prosperously proceed, and reign:” so he does not wish, but does prophesy, who says, “Pour forth Your anger upon the nations which have not known You.”
Which in his usual way he repeats, saying, “And upon the kingdoms which have not called upon Your name.” For nations have been repeated in kingdoms: and that they have not known Him, has been repeated in this, that they have not called upon His name. How then must be understood, what the Lord says in the Gospel concerning stripes, “the many and the few”? If greater the anger of God is against the nations, which have not known the Lord? For in this which he says, “Pour forth Your anger,” with this word he has clearly enough pointed out, how great anger he has willed that there should be understood.
Whence afterwards he says, “Render to our neighbours seven times as much.” Is it not that there is a great difference between servants, who, though they know not the will of their Lord, do yet call upon His name, and those that are aliens from the family of so great a Master, who are so ignorant of God, as that they do not even call upon God? For in place of Him they call upon either idols or demons, or any creature they choose; not the Creator, who is blessed for ever. For those persons, concerning whom he is prophesying this, he does not even intimate to be so ignorant of the will of their God, as that still they fear the Lord Himself; but so ignorant of the Lord Himself, that they do not even call upon Him, and that they stand forth as enemies of His name.
There is a great difference then between servants not knowing the will of their God, and yet living in His family and in His house, and enemies not only setting the will against knowing the Lord Himself, but also not calling upon His name, and even in His servants fighting against it.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)