Calamities remind you of blessings and the One Who bestows them, and cause you to thank and praise Allah for His blessings. Calamities and disasters are a test, and they are a sign of Allah’s love for a person, because they are like medicine: even though it is bitter, despite its bitterness you give it to the one whom you love – and for Allah is the highest description. In the saheeh hadith it says: “The greatest reward comes with the greatest trial. When Allah loves a people He tests them. Whoever accepts that wins His pleasure but whoever is discontent with that earns His wrath.” Narrated by al-Tirmidhi (2396) and Ibn Maajah (4031); classed as hasan by al-Albaani in Saheeh al-Tirmidhi.
Calamities are good for the believer in the sense that reward is stored up as mentioned in a hadith, the Prophet (peace and blessings of Allah be upon him) said: “When Allah wills good for His slave, He hastens the punishment for him in this world, and when Allah wills ill for His slave, he withholds the punishment for his sins from him until he comes with all his sins on the Day of Resurrection.” Narrated by al-Tirmidhi (2396); classed as saheeh by al-Albaani in Saheeh al-Tirmidhi.
Al-Tirmidhi (2399) narrated that Abu Hurayrah (may Allaah be pleased with him) said: The Prophet (peace and blessings of Allah be upon him) said: “Trials will continue to befall the believing man or woman in himself, his child and his wealth until he meets Allah with no sin on him.” Narrated by al-Tirmidhi (2399), classed as saheeh by al-Albaani in al-Silsilah al-Saheehah, 2280.
There are things that will make the calamity easier for him to bear, if the one who is afflicted with calamity thinks about them.
To attain true submission and servitude (‘uboodiyyah) to Allah, the Lord of the Worlds.
Trials prepare the believers to prevail on earth.
Expiation of sins.
Attainment of reward and a rise in status.
Calamities provide an opportunity to think about one's faults and shortcomings and past mistakes.
Calamity is a lesson in Tawheed, faith and trust in Allah.
Calamities drive out self-admiration from our hearts and bring them closer to Allah.
To demonstrate the true nature of people, for there are people whose virtue is unknown until calamity strikes.
Calamities strengthen people’s resolve.
A person becomes able to distinguish between true friends and friends who only have their own interests at heart.
Calamities remind you of your sins so that you can repent from them.
Calamities show you the true nature of this world and its transience, and that it is temporary conveniences, and shows us that true life is that which is beyond this world, in a life in which there is no sickness or exhaustion.
Calamities remind you of the great blessings of good health and ease.
Longing for Paradise.
Remember the words of the Messenger (peace and blessings of Allah be upon him):
“How wonderful is the affair of the believer, for his affairs are all good, and this applies to no one but the believer. If something good happens to him, he is thankful for it and that is good for him. If something bad happens to him, he bears it with patience and that is good for him.” (Narrated by Muslim, 2999).
Through calamity the believer seeks reward, and there is no way to attain it but patience, and there is no way to be patient except with resolute faith and strong will. Calamities shows you in the clearest way the meaning of health and ease that you enjoyed for many years, but did not taste their sweetness or appreciate them fully. You will never long for Paradise until you taste the bitterness of this world. How can you long for Paradise when you are content with this world?
So if calamity befalls a Muslim, he must say Inna Lillaahi wa inna ilayhi raaji’oon (Verily to Allah we belong and unto Him is our return), and say the du’a’s that have been narrated from the Prophet (peace and blessings of Allah be upon him).
How wonderful are those moments in which a person turns to his Lord and knows that He alone is the One Who grants relief from distress.
How great is the relief when it comes after hardship.
Allah says (interpretation of the meaning): “but give glad tidings to As‑ Saabiroon (the patient). Who, when afflicted with calamity, say: ‘Truly, to Allah we belong and truly, to Him we shall return’. They are those on whom are the Salawat (i.e. who are blessed and will be forgiven) from their Lord, and (they are those who) receive His Mercy, and it is they who are the guided ones.” [al-Baqarah 2:155-157]
Rest Allah knows best.
Source: In the shade of the Quran, Sunnah.com, Islam QA