Al-Waaqia • EN-TAFSIR-IBN-ABBAS
﴿ وَإِنَّهُۥ لَقَسَمٌۭ لَّوْ تَعْلَمُونَ عَظِيمٌ ﴾
“and, behold, this is indeed a most solemn affirmation, if you but knew it!”
(And lo! That) i.e. the Qur'an (verily is a tremendous oath, if ye but knew) if you but believe.