No human being on earth is exempted from being subjected to trial and illness. Whether he likes it or not, a test and a tribulation will definitely come. The test, trial, and tribulation will befall all people; whether he is an obedient Muslim or a traitor, rich or poor, one who takes care of his health or does not, is a pious Muslim or an infidel, a man of high status or an ordinary subject.Islam emphasizes that all types of tests and trials/ailments will take effect only by the will of God. Without His will, it is impossible for an illness to affect one's health. Why does God afflict illness upon humans? There are 3 purposes:
1. Expiation of one's sin and upgrading the level of one's devoutness beside God.Illness is not merely considered as misfortune (bad luck) but it is also a blessing from God and the sign of God's love upon us. If we just recite 'zikr,' repentance, solat and etc., we cannot confirm that God will accept these acts of devotion. But if one fallssick, the illness comes to forgive his sins. If he has not committed any sin(s), the illness elevates his rank or level in the Hereafter.
2. Cognizance of one's wrongdoings.God wants to make one realize his delinquency by afflicting an illness upon him. He has probably already been advised by someone or heard a religious lecture, but has not yet changed his heart. Hence, God sends to him an ailment by which he learns a lesson [from God]. That is why some people become aware of their wrongdoings when they fall sick and proceed towards changing their ways. They repent and rectify themselves. They also understand that the illness afflicted was due to their sins. The repentance and penance are the blessings of God.
3. Curse or condemnation of God.If one incurs God's wrath to the extent that God curses him, torment by God will be subjected upon him in the world, and to a larger degree in in the Hereafter. Normally if he receives God's condemnation, the recovery of the illness is very complicated. He might be dying in a very degraded and shameful way. This type of person normally commits more treacherous acts after he recovers from the illness. Even if he has not yet recovered, his evil act is still worse. He is more negligent of God. The ailment destroys his faith. His practice of God's law deteriorates, as he begins to neglect his prayer and act delinquently. This indicates the curse of God upon him. Most people in this category die in a state of degradation.