The heart in Arabic is called al-qalb, which means back and forth. It is called so because the heart is an abstract world (closed area), unique, and developing (developmental). The heart is easy to change, difficult to read, constantly growing, and tidal.
Because it has such properties, then the heart must be well guarded. Because, if not maintained, the heart will turn into a sick heart (al-qalb al-maridh). So many people have intelligent minds, but end up being despicable only because they have a sick heart.
The Prophet SAW said, In the human body there is a lump of flesh, if it is good, then the whole body is good; and if he is damaged, then his whole body is damaged. Know, that’s the heart. (Al-Hadith).
Intelligence that is in the mind, can be defeated by the rot in the heart. Such people will usually be angry at the truth and happy at sleaze. And, if that happens, then that’s the heart is sick. Just like other limbs, a sore heart can be seen from three things. First, the ability of the senses in the heart will be totally lost. Such a heart will become blind, deaf, mute, and paralyzed. He can not distinguish between truth, error, piety, disobedience, and so forth.
Secondly, the ability of the senses in the heart becomes weak. When in fact, the ability of the senses is strong. Just like other members of the body, if you are in a situation like this, the liver means needing nutrition.
Third, the heart cannot see things in their true form. Like seeing the truth becoming heresy, heresy becoming the truth, feeling sweet becoming bitter, and bitter becoming sweet.
Then, how to keep the heart healthy? Ibnul Qayyim explained so that the heart can stay healthy, it can be done in three ways; maintain the strength of the heart, protect the heart from harmful things, and get rid of substances that are harmful to the heart. Heart strength can be obtained from iman. And faith is the main source of strength of the heart. If faith is lost, the heart will become sick.
While to protect the heart from harmful things, it can be done by refraining from sin and immorality. Because these two things can make a heartache. It is the same as poison which if consumed will certainly harm the body.
Finally, in order to stay healthy, substances that harm the liver must be removed. And, the most effective way to get rid of these harmful substances is by repentance and forgiveness. Repentance and forgiveness are two drugs that can get rid of toxins in the liver. He is like an antibody that can make the heart stay healthy.