كَلَّا لَوْ تَعْلَمُونَ عِلْمَ ٱلْيَقِينِ
Kalla law ta'lamoona 'ilmal yaqeen
No indeed! If only you knew for certain.
No indeed! If only you knew with the knowledge of certainty.
The sentence opens with law, if, and never supplies what would follow, an ellipsis Arabic uses when the consequence is too large to state. Commentators filled the gap from the surah's opening: had you known, the race to have more would not have kept you busy. Grammarians pointed out that the next line cannot be the missing answer, since law marks a thing that did not happen, while the seeing promised there is certain.