17:106
وَقُرْءَانًۭا فَرَقْنَٰهُ لِتَقْرَأَهُۥ عَلَى ٱلنَّاسِ عَلَىٰ مُكْثٍۢ وَنَزَّلْنَٰهُ تَنزِيلًۭا
And [it is] a Qur'an which We have separated [by intervals] that you might recite it to the people over a prolonged period. And We have sent it down progressively.
Translation · Saheeh International
Tafsir
Ibn Kathīr (abridged)
The Revelation of the Qur'an in Stages
Allah tells us that His Book, the Glorious Qur'an, has been sent with truth, i.e., it contains the truth, as Allah says:
لَّـكِنِ اللَّهُ يَشْهَدُ بِمَآ أَنزَلَ إِلَيْكَ أَنزَلَهُ بِعِلْمِهِ وَالْمَلَـئِكَةُ يَشْهَدُونَ
(But Allah bears witness to that which He has sent down unto you; He has sent it down with His knowledge, and the angels bear witness) 4:166 meaning, it contains the knowledge which Allah wanted to teach to you, with His rulings, commands and prohibitions.
وَبِالْحَقِّ نَزَلَ
(and with truth it has descended.) means, "It has been sent down to you, O Muhammad, preserved and protected, not contaminated or mixed with anything else, with nothing added or taken away. It has come to you with the truth, brought down by one mighty in power, trustworthy and strong, one who is obeyed by the higher group (angels).'