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)