1 The Title of this eighty-seventh Psalm contains a fresh subject for enquiry: the words occurring here, “for Melech to respond,” being nowhere else found. We have already given our opinion on the meaning of the titles Psalmus Cantici and Canticum Psalmi: and the words, “sons of Core,” are constantly repeated, and have often been explained: so also “to the end;” but what comes next in this title is peculiar. For “Melech” we may translate into Latin “for the chorus,” for chorus is the sense of the Hebrew word Melech....The Passion of our Lord is here prophesied. Now the Apostle Peter says, “Christ also suffered for us, leaving us an example, that we should follow His steps;” this is the meaning of “to respond.” The Apostle John also says, “As Christ laid down His life for us, so ought we also to lay down our lives for the brethren;” this also is to respond. But the choir signifies concord, which consists in charity: whoever therefore in imitation of our Lord's Passion gives up his body to be burnt, if he have not charity, does not answer in the choir, and therefore it profits him nothing. Further, as in Latin the terms Precentor and Succentor are used to denote in music the performer who sings the first part, and him who takes it up; just so in this song of the Passion, Christ going before is followed by the choir of martyrs unto the end of gaining crowns in Heaven. This is sung by “the sons of Core,” that is, the imitators of Christ's Passion: as Christ was crucified in Calvary, which is the interpretation of the Hebrew word Core. This also is “the understanding of Æman the Israelite:” words occurring at the end of this title. Æman is said to mean, “his brother:” for Christ deigns to make those His brethren, who understand the mystery of His Cross, and not only are not ashamed of it, but faithfully glory in it, not praising themselves for their own merits, but grateful for His grace: so that it may be said to each of them, “Behold an Israelite indeed, in whom there is no guile,” just as holy Scripture says of Israel himself, that he was without guile.
2. “O Lord God of my salvation, I have cried day and night before You”. Let us therefore now hear the voice of Christ singing before us in prophecy, to whom His own choir should respond either in imitation, or in thanksgiving.
“O let my prayer enter into Your presence, incline Your ear unto my calling”. For even our Lord prayed, not in the form of God, but in the form of a servant; for in this He also suffered. He prayed both in prosperous times, that is, by “day,” and in calamity, which I imagine is meant by “night.” The entrance of prayer into God's presence is its acceptance: the inclination of His ear is His compassionate listening to it: for God has not such bodily members as we have. The passage is however, as usual, a repetition.
3. “For my soul is filled with evils, and my life draws near unto hell”. Dare we speak of the Soul of Christ as “filled with evils,” when the passion had strength as far as it had any, only over the body?...The soul therefore may feel pain without the body: but without the soul the body cannot. Why therefore should we not say that the Soul of Christ was full of the evils of humanity, though not of human sins? Another Prophet says of Him, that He grieved for us: and the Evangelist says, “And He took with Him Peter and the two sons of Zebedee, and began to be sorrowful and very heavy:” and our Lord Himself says unto them of Himself, “My soul is exceeding sorrowful, even unto death.” The Prophet who composed this Psalm, foreseeing that this would happen, introduces Him saying, “My soul is full of evils, and My life draws near unto hell.” For the very same sense is here expressed in other words, as when He said, “My soul is sorrowful, even unto death.” The words, “My soul is sorrowful,” are like these, “My soul is full of evils:” and what follows, “even unto death,” like, “my life draws near unto hell.” These feelings of human infirmity our Lord took upon Him, as He did the flesh of human infirmity, and the death of human flesh, not by the necessity of His condition, but by the free will of His mercy, that He might transfigure into Himself His own body, which is the Church (the head of which He deigned to be), that is, His members in His holy and faithful disciples: that if amid human temptations any one among them happened to be in sorrow and pain, he might not therefore think that he was separated from His favour: that the body, like the chorus following its leader, might learn from its Head, that these sorrows were not sin, but proofs of human weakness. We read of the Apostle Paul, a chief member in this body, and we hear him confessing that his soul was full of such evils, when he says, that he feels “great heaviness and continual sorrow in heart for his brethren according to the flesh, who are Israelites.” And if we say that our Lord was sorrowful for them also at the approach of His Passion, in which they would incur the most atrocious guilt, I think we shall not speak amiss. Lastly, the very thing said by our Saviour on the Cross, “Father, forgive them, for they know not what they do,” is expressed in this Psalm below, “I am counted as one of them that go down into the pit”: by them who knew not what they were doing, when they imagined that He died like other men, subjected to necessity, and overcome by it. The word “pit” is used for the depth of woe or of Hell. “I have been as a man that has no help.”
Source: The Enarrations, or Expositions, on the Psalms (New Advent)