It is a very strange verse. I saw the book that was published in Qom, it is one thousands and five hundred pages which is the exegesis of the three verses that the first one is “oath”
“By the declining day”
According to some commentators, sin at the time of the revelation of the Holy Quran, when the people of Mecca ate lunch they used to commit sin the whole afternoon and evening. Because Mecca is in the area near the equator and over the years the time distance between the afternoon Azan (Islamic call to prayer) and the evening Azan (Islamic call to prayer). And there is not a big difference between the day and nights there. On the contrary, Our country is in the northern and in the temperate zone. And the amount of hours during the day and the night during the four seasons are different but the days and the nights of Mecca are different.
But just step back and count that the Lord of the universe pledged about the six hours of the afternoon, how much did this amount of time cost? Have you ever thought that how many positive things we can do in this amount of time.
Six hours of studying, writing, working, worshiping, serving the people. Human beings live about eighty years, if we multiply eighty to Three hundred and sixty-five days and nights, then we multiply it to the six hours of the afternoon. Look it will one hundred and seventy-five thousand hours and it is a very extensive time. And have you ever pondered what things can we do in this huge amount of time?
The reason why the lord of the universe takes an oath to this little amount of time is to show how much time is important for him and also wants to tell that he has given this precious thing to you. If you invest this precious thing for me then the business that is mentioned in the Holy Qur'an would happen
source : erfan.ir