Nu’man ibn Bashir relates that the Messenger of Allah ﷺsaid: “Listen carefully, there is a lump of flesh in the body. If it is set right and made good, the entire body becomes good and healthy; but if it becomes diseased, the entire body becomes diseased. Remember well: it is the Heart.”
(Bukhari, Muslim)
In this hadith, the Messenger of Allah (peace and blessings of Allah be to him) highlights the importance of setting our hearts right. Though the heart is a simple lump of flesh, it is in fact pivotal of the entire human body. The health of the heart matters so much to each and every physical organ that if the lump of flesh is set right, the entire body becomes healthy. And, if it is diseased, the entire body gets affected.
The question is how it falls sick and, if so happens, how to set it right. In another hadith, the Messenger of Allah (peace and blessings of Allah be to him) said when a person commits a mistake, a black spot occurs in the heart and gradually the whole heart becomes strained; but, when he regrets and seeks forgiveness from Allah, the black spot is removed. The Blessed Messenger also advised the believers to recite the Holy Qur’ān and remember death profusely in order to keep the heart healthy.
In yet another hadith the Messenger of Allah (peace and blessings of Allah be to him) said thrice: “Remember, piety lies here!” as he pointed his fingers to the heart.