Understanding ,the purpose of creation in a complete sense is beyond man’s innate abilities. Man is a finite created being and cannot reasonably hope to comprehend the action of the infinite creator. Hence ,God made it a part of man’s nature to worship him ,and he sent prophets and books of divine revelation to clarify the aspect of purpose of creation. That purpose is to worship God (ibadah) and the main message of the prophet was to worship God alone, (Tawhid al-Ibadah), Consequently, the gravest sin is shirk , the worship of other instead of Allah or along with Allah