To the end, a psalm song to David.
1. “Christ is the end of the law for righteousness to every one that believes.” For this “end” signifies perfection, not consumption. Now it may be a question, whether every Song be a Psalm, or rather every Psalm a Song; whether there are some Songs which cannot be called Psalms, and some Psalms which cannot be called Songs. But the Scripture must be attended to, if haply “Song” do not denote a joyful theme. But those are called Psalms which are sung to the Psaltery; which the history as a high mystery declares the Prophet David to have used. Of which matter this is not the place to discourse; for it requires prolonged inquiry, and much discussion. Now meanwhile we must look either for the words of the Lord Man after the Resurrection, or of man in the Church believing and hoping on Him.
2. “When I called, the God of my righteousness heard me”. When I called, God heard me, the Psalmist says, of whom is my righteousness. “In tribulation You have enlarged me.” You have led me from the straits of sadness into the broad ways of joy. For, “tribulation and straitness is on every soul of man that does evil.” But he who says, “We rejoice in tribulations, knowing that tribulation works patience;” up to that where he says, “Because the love of God is shed abroad in our hearts by the Holy Ghost, which is given unto us;” he has no straits of heart, they be heaped on him outwardly by them that persecute him. Now the change of person, for that from the third person, where he says, “He heard,” he passes at once to the second, where he says, “You have enlarged me;” if it be not done for the sake of variety and grace, it is strange why the Psalmist should first wish to declare to men that he had been heard, and afterwards address Him who heard him. Unless perchance, when he had declared how he was heard, in this very enlargement of heart he preferred to speak with God; that he might even in this way show what it is to be enlarged in heart, that is, to have God already shed abroad in the heart, with whom he might hold converse interiorly. Which is rightly understood as spoken in the person of him who, believing on Christ, has been enlightened; but in that of the very Lord Man, whom the Wisdom of God took, I do not see how this can be suitable. For He was never deserted by It. But as His very prayer against trouble is a sign rather of our infirmity, so also of that sudden enlargement of heart the same Lord may speak for His faithful ones, whom He has personated also when He said, “I was an hungered, and you gave Me no meat; I was thirsty, and you gave Me no drink,” and so forth. Wherefore here also He can say, “You have enlarged me,” for one of the least of His, holding converse with God, whose “love” he has “shed abroad in his heart by the Holy Ghost, which is given unto us.” “Have mercy upon me and hear my prayer.” Why does he again ask, when already he declared that he had been heard and enlarged? It is for our sakes, of whom it is said, “But if we hope for that we see not, we wait in patience;” or is it, that in him who has believed that which is begun may be perfected?
3. “O you sons of men, how long heavy in heart”. Let your error, says he, have lasted at least up to the coming of the Son of God; why then any longer are you heavy in heart? When will you make an end of crafty wiles, if now when the truth is present ye make it not? “Why do ye love vanity, and seek a lie?” Why would ye be blessed by the lowest things? Truth alone, from which all things are true, makes blessed. For, “vanity is of deceivers, and all is vanity.” “What profit has a man of all his labour, wherewith he labours under the sun?” Why then are you held back by the love of things temporal? Why follow ye after the last things, as though the first, which is vanity and a lie? For you would have them abide with you, which all pass away, as does a shadow.
4. “And know ye that the Lord has magnified his Holy One”. Whom but Him, whom He raised up from below, and placed in heaven at His right hand? Therefore does he chide mankind, that they would turn at length from the love of this world to Him. But if the addition of the conjunction (for he says, “and know ye”) is to any a difficulty, he may easily observe in Scripture that this manner of speech is usual in that language, in which the Prophets spoke. For you often find this beginning, “And” the Lord said unto him, “And” the word of the Lord came to him. Which joining by a conjunction, when no sentence has gone before, to which the following one may be annexed, perhaps admirably conveys to us, that the utterance of the truth in words is connected with that vision which goes on in the heart. Although in this place it may be said, that the former sentence, “Why do ye love vanity, and seek a lie?” is as if it were written, Do not love vanity, and seek a lie. And being thus read, it follows in the most direct construction, “and know ye that the Lord has magnified His Holy One.” But the interposition of the Diapsalma forbids our joining this sentence with the preceding one. For whether this be a Hebrew word, as some would have it, which means, so be it; or a Greek word, which marks a pause in the psalmody (so as that Psalma should be what is sung in psalmody, but Diapsalma an interval of silence in the psalmody; that as the coupling of voices in singing is called Sympsalma, so their separation Diapsalma, where a certain pause of interrupted continuity is marked): whether I say it be the former, or the latter, or something else, this at least is probable, that the sense cannot rightly be continued and joined, where the Diapsalma intervenes.
5. “The Lord will hear me, when I cry unto Him.” I believe that we are here warned, that with great earnestness of heart, that is, with an inward and incorporeal cry, we should implore help of God. For as we must give thanks for enlightenment in this life, so must we pray for rest after this life. Wherefore in the person, either of the faithful preacher of the Gospel, or of our Lord Himself, it may be taken, as if it were written, the Lord will hear you, when you cry unto Him.
6. “Be angry, and sin not”. For the thought occurred, Who is worthy to be heard? Or how shall the sinner not cry in vain unto the Lord? Therefore, “Be angry,” says he, “and sin not.” Which may be taken two ways: either, even if you be angry, do not sin; that is, even if there arise an emotion in the soul, which now by reason of the punishment of sin is not in our power, at least let not the reason and the mind, which is after God regenerated within, that with the mind we should serve the law of God, although with the flesh we as yet serve the law of sin, consent thereunto; or, repent ye, that is, be ye angry with yourselves for your past sins, and henceforth cease to sin. “What you say in your hearts:” there is understood, “say ye:” so that the complete sentence is, “What ye say in your hearts, that say ye;” that is, be ye not the people of whom it is said, “with their lips they honour Me, but their heart is far from Me. In your chambers be ye pricked.” This is what has been expressed already “in heart.” For this is the chamber, of which our Lord warns us, that we should pray within, with closed doors. But, “be ye pricked,” refers either to the pain of repentance, that the soul in punishment should prick itself, that it be not condemned and tormented in God's judgment; or, to arousing, that we should awake to behold the light of Christ, as if pricks were made use of. But some say that not, “be ye pricked,” but, “be ye opened,” is the better reading; because in the Greek Psalter it is κατανύγητε, which refers to that enlargement of the heart, in order that the shedding abroad of love by the Holy Ghost may be received.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)