3 My Mercy and my Refuge, my Upholder and my Deliverer. Much toils this combatant, having his flesh lusting against his spirit. Keep what you have. Then shall you have in full what you wish, when “death shall have been swallowed up in victory;” when this mortal body has been raised, and is changed into the condition of the angels, and rises aloft to a heavenly quality....There is life, there are good days, where nought lusts against the spirit, where it is not said, “Fight,” but “Rejoice.” But who is he that lusts for these days? Every man certainly says, “I do.” Hear what follows. I see that you are toiling, I see that you are engaged in battle, and in danger; hear what follows:...“Depart from evil, and do good:” let not the poor first weep under you, that the poor may rejoice through you. For what reward, since now you are fighting? “Seek peace, and ensue it.” Learn and say, “My Mercy and my Refuge, mine Upholder and my Deliverer, my Protector:” “mine Upholder,” lest I fall; “my Deliverer,” lest I stick; “my Protector,” lest I be stricken. In all these things, in all my toil, in all my battles, in all my difficulties, in Him have I hoped, “who subdues my people under me.” Behold, our Head speaks together with us.
4. “Lord, what is man, that You have become known unto him?”. All is included in “that You have become known unto him.” “Or the son of man, that Thou valuest him?” Thou valuest him, that is, You make him of such importance, You count him of such price, You know under what Thou placest him, over what Thou placest him. For valuing is considering the price of a thing. How greatly did He value man, who for him shed the blood of His only-begotten Son! For God values not man in the same way as one man values another: he, when he finds a slave for sale, gives a higher price for a horse than for a man. Consider how greatly He valued you, that you may be able to say, “If God be for us, who can be against us?” And how greatly did He value you, “who spared not His own Son”? “How shall He not also with Him freely give us all things?” He who gives this food to the combatant, what keeps He in store for the conqueror?...
5. “Man is made like vanity: his days pass away like a shadow”. What vanity? Time, which passes on, and flows by. For this “vanity” is said in comparison of the Truth, which ever abides, and never fails: for it too is a work of His Hand, in its degree. “For,” as it is written, “God filled the earth with His good things.” What is “His”? That accord with Him. But all these things, being earthly, fleeting, transitory, if they be compared to that Truth, where it is said, “I Am That I Am,” all this which passes away is called “vanity.” For through time it vanishes, like stroke into the air. And why should I say more than that which the Apostle James said, willing to bring down proud men to humility, “What is,” says he, “your life? It is even a vapour, which appears for a little time, and then vanishes away.”...Work then, though it be in the night, with your hands, that is, by good works seek God, before the day come which shall gladden you, lest the day come which shall sadden you. For see how safely you work, who art not left by Him whom you seek, “that your Father which sees in secret may reward you openly.”...
6. “Lord, bow Your heavens, and come down: touch the mountains, and they shall smoke”. “Flash Your lightning, and You shall scatter them; send forth Your arrows, and You shall confound them”. “Send forth Your Hand from above, and deliver me, and draw me out of many waters”. The Body of Christ, the humble David, full of grace, relying on God, fighting in this world, calls for the help of God. What are “heavens bowed down”? Apostles humbled. For those “heavens declare the glory of God;” and of these heavens declaring the glory of God it is presently said, “There is neither speech nor language, but their voices are heard among them,” etc. When then these heavens sent forth their voices through all lands, and did wonderful things, while the Lord flashed and thundered from them by miracles and commandments, the gods were thought to have come down from heaven to men. For certain of the Gentiles, thinking this, desired even to sacrifice to them....But they commended to these the Lord Jesus Christ, humbling themselves, that God might be praised; because “the heavens” were “bowed,” that “God” might “come down.”...“Touch the mountains, and they shall smoke.” So long as they are not touched, they seem to themselves great: they are now about to say, “Great are You, O Lord:” the mountains also are about to say, “Thou only art the Most Highest over all the earth.”
Source: The Enarrations, or Expositions, on the Psalms (New Advent)