1 It is said to us, “Praise the Lord”. This is said to all nations, not to us alone. And these words, sounded forth through separate places by the Readers, each Church hears separately; but the one same Voice of God proclaims unto all, that we praise Him. And as though we asked wherefore we ought to praise the Lord, behold what reason he has brought forward: “Praise the Lord,” he says, “for a Psalm is good.” Is this all the reward of them that praise?...The “Psalm” is praise of God. This then he says, “Praise the Lord, for it is good to praise the Lord.” Let us not thus pass over the praise of the Lord. It is spoken, and has passed: it is done, and we are silent: we have praised, and then rested; we have sung, and then rested. We go forth to some business which awaits us, and when other employments have found us, shall the praise of God cease in us? Not so: your tongue praises but for a while, let your life ever praise. Thus then “a Psalm is good.”
Source: The Enarrations, or Expositions, on the Psalms (New Advent)