19 But what do you say, O Asaph, now in understanding? “Deliver not to the beasts a soul confessing to You”....To what beasts, save to those the heads whereof were broken in pieces upon the water? For the same devil is called, beast, lion, and dragon. Do not, he says, give to the Devil and his Angels a soul confessing to You. Let the serpent devour, if still I mind things earthly, if for things earthly I long, if still in the promises of the Old Testament, after the revealing of the New, I remain. But forasmuch as now I have laid down pride, and my own righteousness I will not acknowledge, but Your Grace; against me let proud beasts have no power. “The souls of Your poor forget Thou not unto the end.” Rich we were, strong we were: but You have dried up the rivers of Etham: no longer we establish our own righteousness, but we acknowledge Your Grace; poor we are, hearken to Your beggars. Now we do not dare to lift our eyes to Heaven, but smiting our breasts we say, “O Lord, be merciful to me a sinner.”
20. “Have regard unto Your Testament”. Fulfil that which You have promised: the tables we have, for the inheritance we are looking. “Have regard unto Your Testament,” not that old one: not for the sake of the land of Canaan I ask, not for the sake of the temporal subduing of enemies, not for the sake of carnal fruitfulness of sons, not for the sake of earthly riches, not for the sake of temporal welfare: “Have regard unto Your Testament,” wherein You have promised the kingdom of Heaven. Now I acknowledge Your Testament: now understanding is Asaph, no beast is Asaph, now he sees that which was spoken of, “Behold, the days come, says the Lord, and I will accomplish with the House of Israel and of Juda a new Testament, not after the Testament which I ordered with their Fathers.” “Have regard unto Your Testament: for they that have been darkened have been filled of the earth of unrighteous houses:” because they had unrighteous hearts. Our “houses” are our hearts: therein gladly dwell they that are blessed with pure heart. “Have regard,” therefore, “unto Your Testament:” and let the remnant be saved: for many men that give heed to earth are darkened, and filled with earth. For there has entered into their eyes dust, and it has blinded them, and they have become dust which the wind sweeps from the face of the earth. “They that have been darkened have been filled of the earth of unrighteous houses.” For by giving heed to earth they have been darkened, concerning whom there is said in another Psalm, “Let their eyes be blinded, that they see not, and their back ever bow Thou down.” With earth, then, “they that have been darkened have been filled, with the earth of unrighteous houses:” because they have unrighteous hearts....
21. “Let not the humble man be turned away confounded”. For them pride has confounded. “The needy and helpless man shall praise Your name.” You see, brethren, how sweet ought to be poverty: ye see that poor and helpless men belong to God, but “poor in spirit, for of them is the Kingdom of Heaven.” Who are the poor in spirit? The humble, men trembling at the words of God, confessing their sins, neither on their own merits, nor on their own righteousness relying. Who are the poor in spirit? They who when they do anything of good, praise God, when anything of evil, accuse themselves. “Upon whom shall rest My Spirit,” says the Prophet, “but upon the humble man, and peaceful, and trembling at My words?” Now therefore Asaph has understood, now to the earth he adheres not, now the earthly promises out of the Old Testament he requires not....
Source: The Enarrations, or Expositions, on the Psalms (New Advent)