The best of knowledge in Islam is that of its fundamentals. People's dependence, therefore, on these is above any other dependence. For, the life of a heart depends upon knowledge concerning its Lord and the Object of its worship - in all its details, including His Names, Attributes and Acts. Now, since it is impossible for a man's mind to acquire this knowledge through its own efforts, in all its possible details, Allah's kindness demanded that Messengers be sent with this knowledge, inviting the people to it, giving glad tidings to those who answered the call and warning those who opposed it. Accordingly, the Messengers made this knowledge the central theme of their message. Upon its understanding depends a proper appreciation of their mission. This is followed by two main principles: Firstly, the way to reach it, viz., the understanding of the Shari'ah which deals with sanctions and prohibitions.