Vices cause disease in the heart and soul. Any increase in this disease will cause the death of the soul, i.e. it will cause kufr. Disbelief (shirk), which is the worst of all vices, is a fatal poison for the soul. Some people who do not have belief claim: "My heart is clean. You should look at my heart." Their claim is no more than empty words. A dead heart cannot be clean.

There are many types of disbelief. The worst of all is polytheism. Any variety of a certain vice is mostly specified with its most outstanding characteristic. For that matter, the word shirk used in âyat-i-kerîmas and in (our blessed Prophet's utterances termed) hadîth-i-sherîfs represents all sorts of kufr (disbelief). Allâhu ta'âlâ, in the 48th and 116th âyats of the Sûra Nisâ of the Qur'ân states that He will never forgive the polytheists (mushriks). These verses point out that disbelievers will burn forever in the Hell fire.

["Shirk" means to attribute partners to Allâhu ta'âlâ. A person who does the attributing is called a polytheist and the thing which is attributed is called partner (sharîk). To believe that someone possesses one of the attributes of Divinity means to make him a partner (sharîk). The attributes possessed exclusively by Allâhu ta'âlâ are called "Attributes of Divinity." Some Divine Attributes are the following: Existing eternally, creating, all-knowing, and healing the sick. To believe that a human being or the sun or a cow or any other creature possesses a divine attribute, and thus to respect or beg that being or creature, is said to be to worship them. Those things become an idol. To say words that mean deification of such people or to speak respectfully before statues, pictures or graves of disbelievers assumed to be possessing divine attributes means to worship them and therefore it is polytheism.]