And We reveal of the Qur’an that which is a healing and a mercy to the believers, and it does not add to the unjust save perdition. (17:82)
There is no doubt that man has a spiritual as well as physical wellbeing – the former pertains to the inner or innate and the latter pertains to the outward of a man’s makeup.
According to the Qur’an, true religion is an innate component of mankind’s creation. God says:
So set your face toward the religion upright, the origination (fitra) of Allah according to which He originated mankind. There is no altering Allah’s creation; that is the upright religion, but most people do not know. (30:30)
This innate disposition (fitra) is the greatest asset possessed by a human being and bestowed by Almighty God from His infinite Mercy.
Therefore, depending on the state of one’s fitra (innate disposition), the hearts attain certain conditions.
God has described in the Qur’an that certain believers have a disease in their hearts. When hearts become diseased, they go out of straight nature and deviate from the right path. The heart’s disease means the involvement of the heart with some sort of suspicion and doubt that pollutes the faith in God. It can blend with polytheism as mentioned in 12:106.
And most of them do not believe in Allah without associating others (with Him).
So the heart’s well being or spiritual wellbeing means steadfast and adherence to the right path which leads man to sincerity in belief and eventually to felicity. Hence man has a spiritual health and inward well being just as he has a physical wellbeing that pertains to his outward form. Any disorder in his spiritual wellbeing or health will cause a spiritual disease and illness.
How is the Qur’an a healer of the spiritual diseases?
Tafsir Al-Mizan says:
Through its proofs and arguments, the Qur’an removes every kind of doubt and misunderstanding that one may confront in pursuit of true beliefs and genuine teachings. Through its admonitions, stories, parables, lessons, promises, warnings, threats, glad tidings, laws and prescriptions, the Qur’an dispels the diseases and defects of the hearts. Hence the Qur’an is a healing for the believers.– Allamah Tabataba’i – Al-Mizan English Vol. 25