1 I could wish, brethren, that we were rather listening to our father: but even this is a good thing, to obey our father. Since therefore he who deigns to pray for us, has ordered us, I will speak unto you, beloved, what from the present Psalm Jesus Christ our common Lord shall deign to give us. Now the title of the Psalm is “David's Song of praise.” The “Song of praise” signifies both cheerfulness, in that it is a song; and devotion, for it is praise. For what ought a man to praise more than that which pleases him so, that it is impossible that it can displease him? In the praising of God therefore we praise with security. There he who praises is safe, where he fears not lest he be ashamed for the object of his praise. Let us therefore both praise and sing; that is, let us praise with cheerfulness and joy. But what we are about to praise, this Psalm in the following verses shows us.
2. “O come, let us sing unto the Lord”. He calls us to a great banquet of joy, not one of this world, but in the Lord. For if there were not in this life a wicked joy which is to be distinguished from a righteous joy, it would be enough to say, “Come, let us rejoice;” but he has briefly distinguished it. What is it to rejoice aright? To rejoice in the Lord. You should piously joy in the Lord, if you dost wish safely to trample upon the world. But what is the word, “Come”? Whence does He call them to come, with whom he wishes to rejoice in the Lord; except that, while they are afar, they may by coming draw nearer, by drawing nearer they may approach, and by approaching rejoice? But whence are they afar? Can a man be locally distant from Him who is everywhere?...It is not by place, but by being unlike Him, that a man is afar from God. What is to be unlike Him? It means, a bad life, bad habits; for if by good habits we approach God, by bad habits we recede from God....If therefore by unlikeness we recede from God, by likeness we approach unto God. What likeness? That after which we were created, which by sinning we had corrupted in ourselves, which we have received again through the remission of sins, which is renewed in us in the mind within, that it may be engraved a second time as if on coin, that is, the image of our God upon our soul, and that we may return to His treasures....
3. “Let us make a joyful noise unto God, our salvation.”...Consider, beloved, those who make a joyful noise in any ordinary songs, as in a sort of competition of worldly joy; and you see them while reciting the written lines bursting forth with a joy, that the tongue suffices not to express the measure of; how they shout, indicating by that utterance the feeling of the mind, which cannot in words express what is conceived in the heart. If they then in earthly joy make a joyful noise; might we not do so from heavenly joy, which truly we cannot express in words?
4. “Let us prevent His face by confession”. Confession has a double meaning in Scripture. There is a confession of him who praises, there is that of him who groans. The confession of praise pertains to the honour of Him who is praised: the confession of groaning to the repentance of him who confesses. For men confess when they praise God: they confess when they accuse themselves; and the tongue has no more worthy use. Truly, I believe these to be the very vows, of which he speaks in another Psalm: “I will pay You my vows, which I distinguished with my lips.” Nothing is more elevated than that distinguishing, nothing is so necessary both to understand and to do. How then do you distinguish the vows which you pay unto God? By praising Him, by accusing yourself; because it is His mercy, to forgive us our sins. For if He chose to deal with us after our deserts, He would find cause only to condemn. “O come,” he said therefore, that we may at last go back from our sins, and that He may not cast up with us our accounts for the past; but that as it were a new account may be commenced, all the bonds of our debts having been burnt....The more therefore you despaired of yourself on account of your iniquities, do thou confess your sins; for so much greater is the praise of Him who forgives, as is the fullness of the penitent's confession more abundant. Let us not therefore imagine that we have receded from the song of praise, in understanding here that confession by which we acknowledge our transgressions: this is even a part of the song of praise; for when we confess our sins, we praise the glory of God.
5. “And make a joyful noise unto Him with Psalms.” We have already said what it is “to make a joyful noise:” the word is repeated, that it may be confirmed by the act: the very repetition is an exhortation. For we have not forgotten, so as to wish to be again admonished what was said above, that we should make a joyful noise: but usually in passages of strong feeling a well-known word is repeated, not to make it more familiar, but that the very repetition may strengthen the impression made: for it is repeated that we may understand the feeling of the speaker....Hear now: “For the Lord is a great God, and a great King above all gods” “For the Lord will not cast off His people.” Praise be unto Him, and shouts of joy be unto Him! What people shall He not cast off? We have no right to make our own explanation here: for the Apostle has prescribed this unto us, he has explained whereof it is said. For this was the Jewish people, the people where were the prophets, the people where were the patriarchs, the people begotten according to the flesh from the seed of Abraham; the people in which all the mysteries which promised our Saviour preceded us; the people among whom was instituted the temple, the anointing, the Priest for a figure, that when all these shadows were past, the Light itself might come; this therefore was the people of God; to it were the prophets sent, in it those who were sent were born; to it were delivered and entrusted the revelations of God. What then? Is the whole of that people condemned? Far be it. It is called the good olive-tree by the Apostle, for it commenced with the patriarchs....This then is the tree itself: though some of its boughs have been broken, yet all have not. For if all the boughs were broken, whence is Peter? Whence John? Whence Thomas? Whence Matthew? Whence Andrew? Whence are all those Apostles? Whence that very Apostle Paul who was speaking to us but now, and by his own fruit bearing witness to the good olive? Were not all these of that people? Whence also those five hundred brethren to whom our Lord appeared after His resurrection? Whence were so many thousands at the words of Peter (when the Apostles, filled with the Holy Spirit, spoke with the tongues of all nations) converted with such zeal for the honour of God and their own accusation, that they who first shed the Lord's blood in their rage, learned how to drink it now that they believed? And all these five thousand were so converted that they sold their own property, and laid the price of it at the Apostles' feet. That which one rich man did not do, when he heard from the Lord's mouth, and sorrowfully departed from Him, this so many thousands of those men by whose hands Christ had been crucified, did on a sudden. In proportion as the wound was deeper in their own hearts, with the greater eagerness did they seek for a physician. Since therefore all these were from thence, the Psalm says of them, “For the Lord will not cast off His people.”...
Source: The Enarrations, or Expositions, on the Psalms (New Advent)