And when I am ill, it is He Who heals me. (Surat ash-Shu‘ara', 26:80)
Allah uses illness to force people to realize just how feeble they are and how much help they really need. Thus, the hundreds of diseases in our world are created for both bodily and spiritual purposes. For example, they are signs of a purposeful and superior creation and of His power, for how else can one explain the existence of microscopic viruses?
Only Allah can remove an illness, for He is the One Who created it. As a manifestation of ash-Shafee, Allah removes a disease whenever He wills. If He does not will this, no doctor, advanced technology, or innovative medication can help or cure the patient, for all medicine is only means of recovery. Each illness is sent so that we may ponder upon it, eventually see our Lord's infinite power next to our own feebleness, and seek His help whenever we are in distress. Believers have to be aware that Allah is their only guardian and helper.
The Qur'an praises Prophet Ayyub (as) for his submission to Allah. The moral excellence, patience, and trust he displayed in the face of devastating distress has become an example for all believers. The related verse is as follows:
And Ayyub, when he called out to his Lord: “Great harm has afflicted me, and You are the Most Merciful of the merciful.” (Surat al-Anbiya', 21:83)
Allah answered his call and removed his distress, and Prophet Ayyub (as) earned the rewards of being patient and turning solely to Allah.