8 “For God is the King of all the earth”. What? And before was He not God of all the earth? Is He not God of both heaven and earth, since by Him surely were all things made? Who can say that He is not his God? But not all men acknowledged Him their God; and where He was acknowledged, there only, so to say, He was God. “In Judah is God known.” Not yet was it said to the sons of Korah, “O clap your hands, all you nations.” For that God known in Judah, is King of all the earth: now by all He is acknowledged, for that is fulfilled which Isaiah says, “He is your God who has delivered you, the God of the whole earth shall He be called.” “Sing ye praises with understanding.”
He teaches us and warns us to sing praises with understanding, not to seek the sound of the ear, but the light of the heart. The Gentiles, whence you were called that you might be Christians, adored gods made with hands, and sang praises to them, but not with understanding. If they had sung with understanding, they had not adored stones. When a man sensible sang to a stone insensible, did he sing with understanding? But now, brethren, we see not with our eyes Whom we adore, and yet correctly we adore. Much more is God commended to us, that with our eyes we see Him not. If with our eyes we saw Him, haply we might despise. For even Christ seen, the Jews despised; unseen, the Gentiles adored.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)