Bi ismillahi alrahman al rahim
Allah subhanahu wa t'ala says, "On that day nothing will benefit the human being, neither wealth nor children, only the one who brings Allah a sound heart." A sound heart is one that is free of defects and spiritual blemishes. Though the spiritual heart is centered in the physical heart, the heart being referred to here is the spiritual heart, not the physical heart. In ancient Chinese medicine, the heart houses what is known as "chen" which is "a spirit."
The Chinese character for "thinking," "thought," "love," "virtue," and "intending to listen" all contain the ideogram for the heart. In fact, in every culture in the world, people use metaphors that deal with the heart; in English, we call people who are cruel, "hard-hearted people." There is also the idea of having "a cold heart" and "a warm heart." People who do not hide their emotions well "wear their hearts on their sleeves." When deeply affected, we say, "he affected me in my heart" or "in my core." In fact, the English word "core" means "inner most," and in Arabic, the equivalent "lub" comes from the Latin word, meaning "heart." Thus, the core of the human being is indeed the heart. The word "courage" also comes from the same root word as for "heart" because courage is centered in the heart. The most ancient Indo-European word for heart means "that which leaps." The heart leaps or beats in the breast of man. For example, people say, "my heart skipped a beat" in reaction to seeing somebody. Many such metaphors are used for the heart.
Three Types of People
The ancients were aware of the spiritual diseases of the heart, and this is certainly at the essence of the Islamic teaching. One of the first things the Quran does is define three types of people: the mu'minun, the kafirun, and the munafiqun. The mu'minun are people whose hearts are alive while the kafirun are people whose hearts are dead. The munafiqun are people who have a disease or a sickness in their hearts; thus, Allah subhanahu wa t'ala says, "In their hearts is a disease, and they were increased in their disease." This is also in accordance with another verse: "When their hearts deviated, Allah made them deviate further." When somebody turns away from Allah subhanahu wa t'ala, Allah subhanahu wa t'ala causes them to deviate even further from the truth.
The Heart and the Brain
The actual physical heart in our breast beats at about 100,000 times a day, pumping two gallons of blood per minute, 100 gallons per hour, 24 hours a day, seven days a week, 365 days a year for an entire life time! The vascular system that sends this life-giving blood is over 60,000 miles long: it is more than two times the circumference of the earth. Furthermore, it is interesting to note that the heart starts beating before the brain is formed; the heart begins to beat without any central nervous system. The dominant theory was that the central nervous system is what is controlling the entire human being from the brain, yet we know now that in fact the nervous system does not initiate the heartbeat. It is actually self-initiated; we would say, it is initiated by Allah subhanahu wa t'ala.
The heart is the center of the human being. Many people think the brain is the center of consciousness, yet the Quran clearly states, "They have hearts that they are not able to understand with." According to the Muslims, the center of human consciousness is the heart and not the brain itself, and it is only recently that human beings have learned there are over 40,000 neurons in the heart; in other words, there are cells in the heart that are communicating. Now, it is understood that there is two-way communication between the brain and the heart: the brain sends messages to the heart, but the heart also sends messages to the brain. The brain receives these messages from the heart, which reach the amygdala and the thalamus. The cortex receives input from the amygdala and thalamus that it processes to produce emotion; the new cortex relates to learning and reasoning. These processes are recent discoveries, and although we do not fully understand them, we do know that the heart is an extremely sophisticated organ.
According to the hadith, the heart is a source of knowledge. The Prophet, sallallahu 'alayhi wa sallam, said that wrong action is what irritates the heart. Thus, the heart actually knows wrong actions, and this is one of the reasons why people can do terrible things, but, ultimately, they are affected negatively. In Crime and Punishment, the brilliant Russian author Dostoevsky's indicates that crime itself is the perpetrator's punishment because human beings have to live with the result of their actions: their souls are affected. When people do something against the heart, they act against the soul, and that actually affects human beings to the degree that they will go into a state of spiritual agitation, and people will use many ways to cover this up. This is what kufur is: "kufur" means "covering up." To hide their agitation, people use alcohol, drugs, and sexual experimentation; they also seek power, wealth, and fame, taking themselves into a state of heedlessness, submerging themselves into the ephemeral world which causes them to forget their essential nature and to forget their hearts. Thus, people become cut off from their hearts.
Rasul Allah (sallah llahu alaihi wa sallam) said: "Whoever knows himself, knows his Lord" and whoever knows his Lord has been given His gnosis and nearness.