The Deen of Islam, with all its pillars, rests on the foundation of faith and correct beliefs. If the beliefs of a person are incorrect, but will not cause him to come out from the fold of Islam, then even though he may strive to carry out pious and righteous deeds, he will not receive the promised rewards, as his beliefs, which are the basis of his deeds, are incorrect.

If the beliefs of a person are such that they contradict the fundamental beliefs of Islam (the fundamental beliefs which are required for one to be a Muslim), then even though he outwardly appears to be a believer and carries out the rituals of Islam with the Muslims, since he does not subscribe to the fundamental beliefs of Islam, he will not receive any reward for his good deeds on account of him not being a believer.