12 “In His presence shall fall down the Ethiopians, and His enemies shall lick the earth”. By the Ethiopians, as by a part the whole, He has signified all nations, selecting that nation to mention especially by name, which is at the ends of the earth. By “in His presence shall fall down” has been signified, shall adore Him. And because there were to be schisms in various quarters of the world, which would be jealous of the Church Catholic spread abroad in the whole round world, and again those same schisms dividing themselves into the names of men, and by loving the men under whose authority they had been rent, opposing themselves to the glory of Christ which is throughout all lands; so when He had said, “in His presence shall fall down the Ethiopians,” He added, “and His enemies shall lick the earth:” that is, shall love men, so that they shall be jealous of the glory of Christ, to whom has been said, “Be exalted above the Heavens, O God, and above all the earth Your glory.” For man earned to hear, “Earth you are, and unto earth you shall go.” By licking this earth, that is, being delighted with the vainly talking authority of such men, by loving them, and by counting them for the most pleasing of men, they gainsay the divine sayings, whereby the Catholic Church has been foretold, not as to be in any particular quarter of the world, as certain schisms are, but in the whole universe by bearing fruit and growing so as to attain even unto the very Ethiopians, to wit, the remotest and foulest of mankind.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)