Sin and Crime cannot be categorized as one, since in Shari'ah and law they can be defined differently. Their realms, purposes, composing parts and sanctions differ and this fact makes some theoretical problems when we consider penal law for any kind of sin. To solve these problems one should first understand "sin and punishment" in Islam versus "crime and punishment" in the Western penal law, and then differentiate between them. Another point to take care of is to separate characteristics of Islamic Penal System and the Western one, considering each one's purposes, realms and sanctions. In this way, the rule of "Discretionary punishment for any sin" would not blindly follow, and many theoretical problems of the matter would be solved.