Is tribulation for the thankful believers even if they have not committed sins, or does avoiding sins suffice to avert tribulation? And is delayed marriage a tribulation or a matter of divine decree and destiny?

The interrogative in the noble verse is for the purpose of affirmation to the hypocrites, who are mentioned in the context of the verse. Its meaning is: What benefit would Allah Almighty gain from punishing you if you were grateful and believed? Tribulation (ابتلاء) is for all people, both through good and evil, and it occurs in this worldly life, unlike the torment (عذاب) mentioned in the verse, which refers to the torment of the Hereafter. There is no contradiction between the verse and the authentic hadiths, for tribulation is a test for the patient and grateful believers, to increase their rewards and elevate their ranks. Everything that occurs in life, be it good or evil, is by Allah's decree and destiny, and it is part of tribulation and testing.