The Believers are tested so that it may be known Who is Sincere and Who is Lying

Allah says:

الم

Commentary

وَهُمْ لَا يُفْتَنُونَ (And will not be put to test - 29:2). It is derived from Fitnah, which means trial or test. The believers, especially the prophets and pious, have to go through many a trials in this world. However, they always come out victors in the end. These trials and tribulations sometimes come as a result of enmity of the infidels and sinners by way of afflictions, as have been experienced by the Holy Prophet ﷺ and many other prophets, and at times in the form of diseases, as was experienced by Sayyidna Ayyub (علیہ السلام) . And for others many of these trial types are combined together.