http://thepracticalchristian.net/2009/08/heart-of-darkness/
Humans have a heart of darkness. Left to our own devices, or trusting in anything (idols) other than love from God will trap us there. This true for sinners (all of us) and those who consider themselves saints but trust in traditions more that God. There is only one way to escape a heart of darkness – Christ. Any addition or subtraction will shadow the light from shining in our hearts. Jesus said, “I am the light of the world. Whoever follows me will never walk in darkness, but will have the light of life.” (John 8:12)

Mark 7:6-8, Mark 7:21-24 and John 8:12