my very good brother,
May ALLAH protect you and us from questioning the act of THE MERCIFUL.
The Believer is Patient with the Affliction and thus gains a Reward
Allah informs us that He tests and tries His servants, just as He said in another Ayah:
[وَلَنَبْلُوَنَّكُمْ حَتَّى نَعْلَمَ...