348. Amīr al-mu’minīn, peace be upon him, said: The most serious sin is that which the doer considers light. 
 The result of lack of restraint and care in respect of small sins is that a man becomes rather careless in the matter of sins, and, by and by, this habit produces boldness for larger sins. Then, he begins to commit them without hesitation. Therefore, one should regard small sins as a harbinger of bigger sins, and avoid them, so that the stage for committing big sins does not come.