?O People! Allah, exalted be His remembrance, has only created people so that they might know Him; and when they know Him they worship Him; and when they worship Him they become needless of worshipping others by His worship.' A man asked him, ?O son of the Prophet! May my parents be your ransom, what is meant by knowing Allah?' He replied, 'It is that the people of each era must know their Imam, to whom obedience is mandatory.'