7 But this man rightly understood what mercy he should pray for from God. “Your Mercy, O Lord, is in the Heavens; and Your Truth reaches even to the clouds.” That is, the Mercy which You give to Your Saints, is Heavenly, not earthly; is Eternal, not temporal. And how couldest Thou declare it unto men? Because “Your Truth reaches even unto the clouds.” For who could know the Heavenly Mercy of God, unless God should declare it unto men? How did He declare it? By sending His truth even unto the clouds. What are the clouds? The Preachers of the Word of God....Truth reached even to the clouds: therefore unto us could be declared the Mercy of God, which is in Heaven and not in earth. And truly, Brethren, the clouds are the Preachers of the Word of Truth. When God threatens through His Preachers, He thunders through the clouds. When God works miracles through His Preachers, He lightens through the clouds, He terrifies through the clouds, and waters by the rain. Those Preachers, then, by whom is preached the Gospel of God, are the clouds of God. Let us then hope for Mercy, but for that which is in the Heavens.
8. “Your Righteousness is like the mountains of God: Your Judgments are a great deep”. Who are the mountains of God? Those who are called clouds, the same are also the mountains of God. The great Preachers are the mountains of God. And as when the sun rises, he first clothes the mountains with light, and thence the light descends to the lowest parts of the earth: so our Lord Jesus Christ, when He came, first irradiated the height of the Apostles, first enlightened the mountains, and so His Light descended to the valley of the world. And therefore says He in a certain Psalm, “I lifted up my eyes unto the mountains, from whence comes my help.” But think not that the mountains themselves will give you help: for they receive what they may give, give not of their own. And if you remain in the mountains, your hope will not be strong: but in Him who enlightens the mountains, ought to be your hope and presumption. Your help indeed will come to you through the mountains, because the Scriptures are administered to you through the mountains, through the great Preachers of the Truth: but fix not your hope in them. Hear what He says next following: “I lifted up my eyes unto the mountains, from whence comes my help.” What then? Do the mountains give you help? No; hear what follows, “My help comes from the Lord, which made Heaven and earth.” Through the mountains comes help, but not from the mountains. From whom then? “From the Lord, which made Heaven and earth.”...
9. “Your Judgments are like the great abyss.” The abyss he calls the depth of sin, whither every one comes by despising God; as in a certain place it is said, “God gave them over to their own hearts' lusts, to do the things which are not convenient.”...Because then they were proud and ungrateful, they were held worthy to be delivered up to the lusts of their own hearts, and became a great abyss, so that they not only sinned, but also worked craftily, lest they should understand their iniquity, and hate it. That is the depth of wickedness, to be unwilling to find it out and to hate it. But how one comes to that depth, see; “Your Judgments are the great abyss.” As the mountains are by the Righteousness of God, who through His Grace become great: so also through His Judgments come they unto the depth, who sink lowest. By this then let the mountains delight you, by this turn away from the abyss, and turn yourself unto that, of which it is said, “My help comes from the Lord.” But whereby? “I have lifted up my eyes unto the mountains.” What means this? I will speak plainly. In the Church of God you find an abyss, you find also mountains; you find there but few good, because the mountains are few, the abyss broad; that is, you find many living ill after the wrath of God, because they have so worked that they are delivered up to the lusts of their own heart; so now they defend their sins and confess them not; but say, Why? What have I done? Such an one did this, and such an one did that. Now will they even defend what the Divine Word reproves. This is the abyss. Therefore in a certain place says the Scripture (hear this abyss), “The sinner when he comes unto the depth of sin despises.” See, “Your Judgments are like the great abyss.” But yet not are you a mountain; not yet are you in the abyss; fly from the abyss, tend towards the mountains; but yet remain not on the mountains. “For your help comes from the Lord, which made Heaven and earth.”
Source: The Enarrations, or Expositions, on the Psalms (New Advent)