Ibn al-Qayyim says "Every muscle in the body was created to execute a specific function, by which, it can obtain the pinnacle of its performance. And the sickness of that particular body part is its failure to execute the function for which it was created or having some level of deficiency in performing it, if it even functions at all.
The sickness of the hand is its inability to grab. The sickness of the eye is its inability to see. The sickness of the tongue is its inability to utter. The sickness of the body is its inability to move in the natural order it was created to or its deficiency in doing do.
The sickness of the heart is its inability to execute the functions it was created to perform such as; being conscious of Allah, knowing Allah, loving Allah, desiring to meet Allah and turning constantly towards Him, while giving precedence to this over the heart’s every ardent desire.
Consequently, if the slave knows everything else but fails to know Allah, it is as if he knows absolutely nothing. Even if he achieves some share or portion of what this transient life has to offer from its many pleasures and desires but fails to develop a solid intimate relationship with Allah which produces an ardent desire to meet Him emerging from a strong love of Him, then he has failed to achieve the bliss this life has to offer as well as forfeited the ultimate pleasure of his eye.
Rather if the heart is completely void of the knowledge of Allah and the desire to meet Him, then all of what he obtained from the pleasures and delights of this life will inevitably become a punishment for him"
Ref: Ighatha tul Lahfan min Masayid ush Shaytan