56:76

وَإِنَّهُ لَقَسَمٌ لَّوْ تَعْلَمُونَ عَظِيمٌ

Transliteration:

Wa-innahu laqasamun law taAAlamoona AAatheemun

Word by Word:

And indeed, it (is) surely an oath, if you know - great,

Translations:

and, behold, this is indeed a most solemn affirmation, if you but knew it!

And that is indeed a mighty adjuration if ye but knew,-

And lo! that verily is a tremendous oath, if ye but knew -

And it is a great oath indeed, if you knew --

And indeed, it is an oath - if you could know - [most] great.