The Prophet Muhammad (pbuh) is reported to have said about the believers, “When the wind comes to them, it makes them bend. When it is still, they are upright. That is how it is with the believer. He bends with affliction. The unbeliever is like the sturdy cedar which stands straight until Allah makes it snap.” [Muslim]
It means that the believer is stricken and suffers affliction and illness but he is pleased with how he is used by the decrees of Allah, obeying them, yielding to them with pleasure and lack of wrath, as the tender plants of the fields obey and submit to the wind, and bend when the winds blow. Then Allah removes the winds of affliction from the believer and makes him straight and healthy as the tender plants of the fields are straight when the air is still. The believer returns to gratitude towards His Lord and recognition of the blessing He has shown him by removing the affliction. He waits for mercy and reward to come to him. When this is the case, the final illness is not hard for him and its throes and agony are not intense for him because he has accustomed himself by means of earlier pains and he recognises the reward which it contains. He has adjusted himself to misfortune, fragility and weakness by the continuation of illness or its intensity.
The unbeliever is different. He is well in most states and strong and healthy in his body, like the sturdy cedar, until Allah desires to destroy him and snaps him immediately while he is unaware and takes him suddenly without kindness or compassion. His death is a more intense grief for him and enduring its throes is a more intense pain and punishment in spite of his strength and healthy body. The punishment of the Next World is more intense. It is like uprooting the cedar. It is as Allah says, “Then We seized them suddenly when they were not expecting it” (Qur’an 7:95).
Source: Al-Shifa by Qadhi ‘Iyaadh