﴿ كَلَّا لَوْ تَعْلَمُونَ عِلْمَ ٱلْيَقِينِ ﴾

“Nay, if you could but understand [it] with an understanding [born] of certainty,”

(Nay, would that ye knew (now)) what will be done to you on the Day of Judgement (with a sure knowledge!) what you bragged about in the life of the world!