3 But perhaps Scripture meant us to consider in the stag not this point only, but another also. Hear what else there is in the hart. It destroys serpents, and after the killing of serpents, it is inflamed with thirst yet more violent; having destroyed serpents, it runs to “the water-brooks,” with thirst more keen than before. The serpents are your vices, destroy the serpents of iniquity; then will you long yet more for “the Fountain of Truth.” Perhaps avarice whispers in your ear some dark counsel, hisses against the word of God, hisses against the commandment of God. And since it is said to you, “Disregard this or that thing,” if you prefer working iniquity to despising some temporal good, you choose to be bitten by a serpent, rather than destroy it. Whilst, therefore, you are yet indulgent to your vice, your covetousness or your appetite, when am I to find in you “a longing” such as this, that might make you run to the water-brooks?...
Source: The Enarrations, or Expositions, on the Psalms (New Advent)