Surprise! – it’s not the perfect man who is blessed – it’s the forgiven sinner?! A truly righteous and upright man (v 11) is the one who honestly confesses his sin and is forgiven (v 2). This irritates the Pharisee in every single human in history because it discounts our own goodness.
The darkness/sickness/fear that surrounds unconfessed sin and guilt is the mercy of God. It is his hand that is crushing us in order to turn us towards repentance (v 4).
There is a contrast between the one who tries to cover his own guilt and the LORD’s true covering of our iniquity. When we keep our sin “hidden”, it eats us. But when we bring it out of hiding and confess it to the LORD, he protects us from it. The hiding place in verse 7 is covenantal: there are no outside enemies here who are trying to attack David – it’s his own sin that is killing him!
The shouts/songs of deliverance are key here. God actually enjoys forgiving sinners. He sings about it. It glorifies him as the True Deliverer, the True Savior. Coming to Him while knowing ourselves to be sinners is an invitation, not a threat.
Given this, the comparison to a mule is humbling – why is our instinct to run and hide our sin from God? He is our only hope of covering. He has shown this to every human from Adam on down the line.
The only way to be righteous is to confess our unrighteousness. The only way for our sin to be covered is for it to be uncovered.