﴿ وَقُرْءَانًۭا فَرَقْنَٰهُ لِتَقْرَأَهُۥ عَلَى ٱلنَّاسِ عَلَىٰ مُكْثٍۢ وَنَزَّلْنَٰهُ تَنزِيلًۭا ﴾

“[bearing] a discourse which We have gradually unfolded, so that thou might read it out to mankind by stages, seeing that We have bestowed it from on high step by step, as [one] revelation.”

And it is a Qur’ān qur’ānan is in the accusative because of the verb governing it which is the following that We have divided that We have revealed in portions over 20 or 23 years that you may recite it to mankind at intervals gradually and with deliberateness so that they are able to comprehend it and We have revealed it by successive revelation one part after another according to what is best for mankind.