Faith is perhaps mostly related with devotion in the heart and conviction in the mind both of which are abstract phenomena. Nevertheless, most duties in all religions call for physical cleanliness before or during the observation of a certain ritual. Cleanliness in Islam defines physical cleanliness in detail, for it is an obligation and a component of prescribed prayers in Islamic practice.

Cleanliness has a lot to do with keeping ourselves and our environment safe from all kinds of filth. The book also gives prominence to the spiritual dimensions of cleanliness, like purifying the heart from what is bad and evil and keeping one's earnings untainted with illegitimate income. It emphasizes that purifying from physical filth and keeping the heart safe from spiritual impurities—such as false beliefs and doctrines, associating partners with God, hypocrisy, and other sins—are all religious and moralistic tasks that are inherent in humankind.