Sins Blacken the Heart

The first tradition is reported from Imam Ja'far as-Sadiq (a.s.): He said,
"There is no man who does not have a white spot in his heart. When he commits a sin a black spot emerges from this spot. If he repents, the blackness goes away but if he sinks in sin and continues to sin the blackness keeps on increasing till it surrounds the whiteness of the heart completely. When the white spot is totally covered by the blackness, the owner of this heart will never revert towards goodness. This tradition is in consonance with the utterance of Allah:
"By no means! But on their hearts is the stain of the (ill) which they do."
(Surah Mutaffefeen 83:14)

The Blackened Heart is Immune to Advice and Counsel

The people with the 'blackened heart' are totally unaffected by any counsel because their sins have caused the darkness to spread all over their heart. The loss of the inner eye prevents them from perceiving truths nor can they recognise the truth when they see it. They cannot accept any exhortation and revert to the path of virtue. It is in this connection that Imam Ja'far as-Sadiq (a.s.) explains:
"A man resolves to perform a sinful action but does not act upon it, but sometimes does commit it; Allah sees him and says: "By My Glory, after this I shall never forgive you."

According to another report, the person (sinner) is kept away from the Mercy of Allah due to his sin. He also does not get the impetus to seek repentance, hence his sin is never forgiven. Allama Majlisi (r.a.) writes in the explanatory note of the above tradition: "The purport of this tradition of Imam Ja'far as-Sadiq (a.s.) is that, the Imam has commanded us to fear all types of sins because every sin seems to be such that it may not qualify being overlooked. 

- Greater Sins, Vol.1