بَلْ هُوَ ايَاتٌ بَيِّنَاتٌ فِي صُدُورِ الَّذِينَ أُوتُوا الْعِلْمَ
Nay, but it is (Quran), the clear Ayat, (preserved) in the breasts of those who have been given knowledge.
meaning, this Qur'an is clear Ayat which indicate the truth, commands, prohibitions and stories. It is memorized by the scholars for whom Allah makes it easy to memorize, recite and interpret.
This is like the Ayah,
وَلَقَدْ يَسَّرْنَا الْقُرْءَانَ لِلذِّكْرِ فَهَلْ مِن مُّدَّكِرٍ
And We have indeed made the Qur'an easy to understand and remember; then is there any one who will remember! (54;17)
The Messenger of Allah said;
مَا مِنْ نَبِيَ إِلاَّ وَقَدْ أُعْطِيَ مَا امَنَ عَلَى مِثْلِهِ الْبَشَرُ وَإِنَّمَا كَانَ الَّذِي أُوتِيتُهُ وَحْيًا أَوْحَاهُ اللهُ إِلَيَّ فَأَرْجُو أَنْ أَكُونَ أَكْثَرَهُمْ تَابِعًا
There has never been any Prophet who was not given that which would make people believe in him. What I have been given is revelation which Allah reveals to me, and I hope that I will have the most followers among them.
According to the Hadith of `Iyad bin Himar, recorded in Sahih Muslim, Allah says;
إِنِّي مُبْتَلِيكَ وَمُبْتَلٍ بِكَ وَمُنْزِلٌ عَلَيْكَ كِتَابًا لَا يَغْسِلُهُ الْمَاءُ تَقْرَوُهُ نَايِمًا وَيَقْظَانًا
"I am testing you and testing others through you, revealing to you a Book which cannot be washed away by water, which you recite while you are asleep and while you are awake."
This means, if the manuscript where it is written were to be washed with water, there is no need for that manuscript. This is because it is preserved in the hearts and is easy on the tongue (i.e., is easy to recite), and is controlling people's hearts and minds. It is miraculous in its wording and in its meanings.
In the previous Scriptures this Ummah was described as carrying their holy Books in their hearts.
وَمَا يَجْحَدُ بِأيَاتِنَا إِلاَّ الظَّالِمُونَ
And none but the wrongdoers deny Our Ayat.
Nobody denies it or tries to undermine its status or rejects it except the wrongdoers, i.e., the arrogant transgressors who know the truth but turn away from it, as Allah says;
إِنَّ الَّذِينَ حَقَّتْ عَلَيْهِمْ كَلِمَةُ رَبِّكَ لَا يُوْمِنُونَ
وَلَوْ جَأءَتْهُمْ كُلُّ ءايَةٍ حَتَّى يَرَوُاْ الْعَذَابَ الاٌّلِيمَ
Truly, those, against whom the Word (wrath) of your Lord has been justified, will not believe. Even if every sign should come to them, until they see the painful torment. (10;96-97