The Problem of Unconfessed Sin

This is from Gospel Centered Discipleship by Jonathan Dodson (p. 66-67), which I am reading with my elders:

Those who avoid confession surrender the fight.  This unfortunately surrenders leads to sick disciples who hobble along in unbelief, refusing to believe God's promise of healing in confession: "Therefore confess your sins to one another and pray for one another, that you may be healed" (James 5:16).  When we avoid confession and prayer, we dont think of ourselves as cowardly or indifferent to grace.   In fact, when we lack an earnest faith, we dont always appear sick.  We may seem very normal, cordial with others, regular in church attendance, even fun to be around.  But like an undiagnosed cancer patient, we carry on everyday life ignorant of the deadly disease growing inside of us - unconfessed sin.  In Psalm 32:3-4, David poignantly describes the effect of unconfessed sin:

For when I kept silent, my bones wasted away

through my groaning all day long.

 For day and night your hand was heavy upon me;

my strength was dried up as by the heat of summer.