9 “God shall reign over all nations”. Who reigned over one nation, “shall reign” (says He) “over all nations.” When this was said, God reigned over one nation. It was a prophecy, the thing was not yet shown. Thanks be to God, we now see fulfilled what before was prophesied. A written promise God sent unto us before the time, the time fulfilled He has repaid us. “God shall reign over all nations,” is a promise. “God sits upon His Holy Seat.” What then was promised to come, now being fulfilled, is acknowledged and held. “God sits upon His Holy Seat.” What is His Holy Seat? Haply says one, The Heavens, and he understands well. For Christ has gone up, as we know, with the Body, wherein He was crucified, and sits at the right hand of the Father; thence we expect Him to come to judge the quick and the dead. “God sits upon His Holy Seat.” The Heavens are His Holy Seat. Will you also be His Seat? Think not that you can not be; prepare for Him a place in your heart. He comes, and willingly sits. The same Christ is surely “the Power of God, and the Wisdom of God:” and what says the Scripture of Wisdom Herself? The soul of the righteous is the seat of Wisdom. If then the soul of the righteous is the seat of Wisdom, be your soul righteous, and you shall be a royal seat of Wisdom. And truly, brethren, all men who live well, who act well, converse in godly charity, does not God sit in them, and Himself command? Your soul obeys God sitting in it, and itself commands the members. For your soul commands your members, that so may move the foot, the hand, the eye, the ear, and itself commands the members as its servants, but yet itself serves its Lord sitting within. It cannot well rule its inferior, unless its superior it have not disdained to serve.
10. “The princes of the peoples are gathered together unto the God of Abraham”. The God of Abraham, and the God of Isaac, and the God of Jacob. True it is, God said this, and thereupon the Jews prided themselves, and said, “We are Abraham's children;” priding themselves in their father's name, carrying his flesh, not holding his faith; by seed cleaving to Him, in manners degenerating. But the Lord, what said He to them so priding themselves? “If you are Abraham's children, do the works of Abraham.” Again...“The princes of the peoples:” the princes of the nations: not the princes of one people, but the princes of all people have “gathered together unto the God of Abraham.” Of these princes was that Centurion too, of whom but now when the Gospel was read ye heard. For he was a Centurion having honour and power among men, he was a prince among the princes of the peoples. Christ coming to him, he sent his friends to meet Him, nay unto Christ truly passing over to him he sent his friends, and asked that He would heal his servant who was dangerously sick. And when the Lord would come, he sent to Him this message: “I am not worthy that You should enter under my roof, but say in a word only, and my servant shall be healed.” “For I also am a man set under authority, having under me soldiers.” See how he kept his rank! First he mentioned that he was under another, and afterwards that another was under him. I am under authority, and I am in authority; both under some I am, and over some I am....As though he said, If I being set under authority command those who are under me, You who is set under no man's authority, canst not Thou command Your creature, since all things were made by You, and without You was nothing made. “Say,” then, said he, “in a word, and my servant shall be healed. For I am not worthy that You should enter under my roof.”...Admiring at his faith, Jesus reprobates the Jews' misbelief. For sound to themselves they seemed, whereas they were dangerously sick, when their Physician not knowing they slew. Therefore when He reprobated, and repudiated their pride what said he? “I say unto you, that many shall come from the east and west,” not belonging to the kindred of Israel: many shall come to whom He said, “O clap your hands, all you nations;” “and shall sit down with Abraham, and Isaac, and Jacob, in the kingdom of heaven.” Abraham begot them not of his own flesh; yet shall they come and sit down with him in the kingdom of heaven, and be his sons. Whereby his sons? Not as born of his flesh, but by following his faith. “But the children of the kingdom,” that is, the Jews, “shall be cast into outer darkness, there shall be weeping and gnashing of teeth.” They shall be condemned to outer darkness who are born of the flesh of Abraham, and they shall sit down with him in the kingdom of heaven, who have imitated Abraham's faith.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)