A person should have full conviction that Allâh Ta'âla loves us more than what our own mothers love us. Whatever He does is solely for our benefit. When we are afflicted by any sickness, our sins are wiped out. When we exercise patience, our stages are increased and calamities are withheld from us. Whatever pride and arrogance that we may have is decreased and we realize our dependence on Allâh Ta'âla.
Previously, a person may have been very independent. When he falls ill, he realizes his dependence on others for every little thing. When he was healthy and strong he may have not valued his health. Once he falls ill, he realizes the importance of health, appreciates it and later expresses his gratitude.
In short, illness is a source of mercy for us Muslims. In fact, it is a great bounty from Allâh Ta'âla. At the same time, it is a great test and trial from Allâh Ta'ala. We have to exercise patience, express our gratitude and consider everything to be the decree of Allâh. We should not express evil words against Allâh Ta'âla and whatever He has decreed. At times such words could cause us to become devoid of Imân.
Just think, that here is the person who has borne so many difficulties (for which he would have been rewarded) but has allowed all the rewards to be snatched away from him. He has spent some money (on medication), but because of the evil words that he has uttered, he lost his Imân, lost the world, and lost his Dîn. If, Allâh forbid, he does not repent and passes away in this state, he has lost his entire life earnings of Imân on account of a little suffering. May Allâh save us from this.