Surah Al-Mutaffifin Verse 14

6017 The heart of a man, as created by Allah, is pure and unsullied. Every time that a man does an ill deed, it marks a stain or rust on his heart. But on repentance and forgiveness, such stain is washed off. If there is no repentance and forgiveness, the stains deepen and spread more and more, until the heart is sealed (2:7), and eventually the man dies a spiritual death. It is such stains that stand in the way of his perceiving Truths which are obvious to others. That is why he mocks at Truth and hugs Falsehood to his bosom.