The folly of dealing with sin on the outside instead of the inside

"...A man may beat down the bitter fruit from an evil tree, until he is weary; whilst the root abides in strength and vigour, the beating down of the present fruit will not hinder it from bringing forth more. This is the folly of some men. They set themselves with all earnestness and diligence against the appearing eruption of lust; but leaving the principle and root untouched, perhaps unsearched out, they make but little or no progress in this work of mortification..."
~John Owen, Mortification of Sin (p.68)