As was explained concerning the meaning of divine determining, known as destiny, in the Twenty-Sixth Word, men have no right to complain in the case of disasters and illness for the following three reasons: 

First Reason: Allah Most High has made the garment of the body with which He has clothed man a manifestation of His art. He has made man to be a model on which He cuts, trims, alters and changes the garment of the body, thus displaying the manifestation of various of His names. Just as the name of Healer makes it necessary that illness should exist, so too the name of Provider requires that hunger should exist. And so on.

مَالِكُ الْمُلْكِ يَتَصَرَّفُ فِى مُلْكِهِ كَيْفَ يَشَۤاءُ

Second Reason: It is by means of disasters and sicknesses that life is refined, perfected, strengthened and advanced; that it yields results, attains perfection and fulfils its own purpose. Life led monotonously on the couch of ease and comfort resembles not so much the pure good that is being, as the pure evil that is non-being; it tends in fact in that direction. 

Third Reason: This worldly realm is the field of testing, the abode of service. It is not the place of pleasure, reward, and requital. Considering, then, that it is the abode of service and place of worship, sicknesses and misfortunes – as long as they do not affect belief and are patiently endured – conform fully to service and worship, and even strengthen it. Since they make each hour’s worship equivalent to that of a day, one should offer thanks instead of complaining. Worship consists in fact of two kinds, positive and negative. What is meant by the positive is obvious. As for negative worship, this is when one afflicted with misfortune or sickness perceives his own weakness and helplessness, and turning to his Compassionate Lord, seeks refuge in Him, meditates upon Him, petitions Him, and thus offers a pure form of worship that no hypocrisy can penetrate. If he endures patiently, thinks of the reward attendant on misfortune and offers thanks, then each hour that he passes will count as a whole day spent in worship. His brief life becomes very long. There are even cases where a single minute is counted as equal to a whole day’s worship.

I once was extremely anxious because of an awesome illness that struck one of my brothers of the hereafter, Muhajir Hafız Ahmed. But then a warning came to my heart: “Congratulate him!” Each minute he spends is counted as a whole day’s worship. He was in any event enduring his illness in patience and gratitude.   

Source: 2nd Flash, Risale-i Nur Collection