This very thread is open for that.
Thought the opposite for where it has been posted.
Suffering is the part of life and the Islamic teaching about suffering is that it happens for four major reasons.
1- Test for the believers.
29:2 [29:2] Do the people think that they will be left to say, "We believe," without being put to the test?
[29:3] We have tested those before them, for God must distinguish those who are truthful, and He must expose the liars.
also:
[2:155] We will surely test you through some fear, hunger, and loss of money, lives, and crops. Give good news to the steadfast.
To pass the test, the believer must maintain his trust that God only can relieve his hardship. The believer will maintain his prayer and call onto God:
[27:62] Who is the One who rescues those who become desperate and call upon Him, relieves adversity, and makes you inheritors of the earth? Is it another god with God? Rarely do you take heed.
2- Hardship and adversity is also decreed by God as a purifying of our souls
3- Suffering through hardship and adversity is also a reminder for people who tend to take things for granted and forget all of God’s blessings.
[14:34] If you count God's blessings, you can never encompass them. Indeed, the human being is transgressing, unappreciative.
[41:51] When we bless the human being, he turns away, and drifts farther and farther away, and when he suffers any affliction, he implores loudly.
[10:23] But as soon as He saves them, they transgress on earth, and oppose the truth. O people, your transgression is only to the detriment of your own souls. You remain preoccupied with this worldly life, then to us is your ultimate return, then we inform you of everything you had done.
4- Better ranking in heaven because of patience
2:45 Nay, seek (Allah's) help with patient perseverance and prayer: It is indeed hard, except to those who bring a lowly spirit,-
2:155 And We will surely test you with something of fear and hunger and a loss of wealth and lives and fruits, but give good tidings to the patient,
3:200 O you who believe! Endure and be more patient (than your enemy), and guard your territory by stationing army units permanently at the places from where the enemy can attack you, and fear Allah, so that you may be successful.
The prophets are people who suffered the most, being expelled by their people for their message. However, they have the highest ranks in heaven.
Patience is one of the keys to heaven in Islam
2:45 And seek help through patience and prayer, and indeed, it is difficult except for the humbly submissive [to Allah ]
2:153 O you who have believed, seek help through patience and prayer. Indeed, Allah is with the patient.