The the Religious Sciences, which is widely considered as greatest work of Islamic spirituality. Written by the most famous of time, Book the Lawful and the Unlawful unlike other Islamic works concerned with legal issues. Here, Abu Hamid al-Ghazali aims teach readers firstly the theory of is lawful what unlawful and how deal with dubious or ambiguous issues, secondly how apply the knowledge they have gained their everyday lives. The main support this application, especially in that unclear, is caution prudence (ward) Ghazali explains the degrees of prudence necessary beginning with prudence of the upright ending the prudence saintly. Thus sincere practice what is lawful and desisting from what unlawful become integrated into spiritual life. As his other works, Ghazali bases himself the Qur an and narrations from the Prophet Muhammad, followed by examples the Companions, the Successor generations and pious Predecessors. In new edition, Islamic Texts Society has included translation Imam Ghazali s own Introduction to the Revival the Religious Sciences which gives the that caused to write the work, structure of whole of the Revival and places each of the chapters in the context of the others.