“My wounds stink and fester because of my foolishness, I am utterly bowed down and prostrate; all the day I go about mourning. For my sides are filled with burning, and there is no soundness in my flesh. I am feeble and crushed; I groan because of the tumult of my heart.” -Psalm 38:5–8
Behold a truly penitent man, one who recognizes and acknowledges the stench and putridness of his foolishness. He is humbled as low as one can be humiliated, to the point that all he can do is mourn and groan. And his heart is so heavy that it adds to his pain and physical suffering.
May God grant us such humility that we are able to see the depth and gravity of our own foolishness that we might fully repent of it as David did.
Foolishness is defined in Scripture as he who says in his heart, “There is no God” (Psalm 14:1 cf. Psalm 53:1). It is interesting the St. Anselm reasoned out that to say there is no God is self-contradictory because when we speak of God in this manner we are speaking of that than which there is nothing greater in existence. By thinking of the very person of God in order to say he doesn’t exist, we are acknowledging that at the very least he exists in our imagination. And if he exists in our imagination, he must, by definition of his person (that than which there is nothing greater in existence), he must therefore exist in reality and not only in our imagination.
Granted, it may take some time to reread and think on that complicated formula (called the ontological argument in theology) for a moment, but the point is whenever we sin, we do so as believers who in that moment of our sinning deny God, and do so in a most self-contradictory way.
All that to say, sin is irrational by definition—which is why the Psalmist recognizes it as foolishness. And until we see our sin as that which it really is, foolishness in the biblical sense, perhaps we are not fully repentant.
But thanks be to God, Jesus died and rose again, even for our deficient repentance. And in our moments of foolishness, we are (in Christ) still blessed (accepted, KJV) in the Beloved (Ephesians 1:6).