When David prayed in Psalm 51:10, "create in me a clean heart, and renew a right spirit within me" this displayed three things: his acknowledgment that he, his core being, was a sinner; his repentance, in turning to God, he displayed faith in God's ability to resurrect a new spirit with in him. Only a cleansed heart can decide (literally 'to cut off') so clean does not necessarily denote sinless because at this point, the cleansing enables the individual to "decide" between the choices of cutting off oneself for God or to cut off God for oneself (this is by grace); and three, he displayed his decision for God asking for a right spirit (this is through faith).