Ibnul Uthaymeen said,
“If a person does not strive in curing the sickness of his heart, then verily he will be inflicted with an increase in its sickness due to the statement of Allah,
‘In their hearts is a disease (of doubt and hypocrisy) and Allah has increased their disease’ [2:10]
There is no doubt that this infliction is greater than that of losing a child, family member, or wealth. Many of the people are heedless of it for many of the people think that being inflicted only occurs in affairs that are apparent such as the bodies, wealth, and children.
The reality is that being inflicted with the sickness of the heart and its corruption is more severe and greater than being inflicted with similar to those affairs. Rather, many of the people’s hearts are dead. One [of these types of people] is afflicted with fear, hunger and other than that from afflictions which are materialistic and felt yet despite that one does not abstain from that which one is upon of evil acts and sins.” End translation. [Rulings from the Quran v.1 pg.87]
Majid Jawed Al-Afghanee