hence his sin is never forgiven

"The (sinner) person is kept away from the Mercy of Allah (S.w.T.) due to his sin. He also does not get the impetus to seek repentance, hence his sin is never forgiven. Allama Majlisi (R) writes in the explanatory note of the above tradition: 'The purport of this tradition of Imam Ja’far as-Sadiq (A) 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 to be overlooked.'"