The diseases of the heart differ from the diseases of the organs. Diseases of the organs present symptoms to alert people of the pain felt, whereas diseases of the heart do not.
Thus, a person might be corrupted but thinks himself virtuous, or he might be miserly but says “No one is more generous than me!”, or he might be a wrong-doer but says, “No one is more guided than me!” or he might say: “I do not feel envy towards anyone!” when in reality, he is of the most envious people of all.
Therefore, the diseases of the heart such as conceit, arrogance, spite and rancour do not show symptoms of their presence.
As such, the hypocrites have diseases in their hearts but they do not perceive them. The first reason for this is the lack of harmony between their faculties. Among the faculties a person has are the speech faculty and the belief faculty. If he portrays a picture but conceals another, it indicates that there is a lack of harmony between these faculties. This lack of harmony is actually a disease of the heart.