You only mention 2 points:

 

1- That it is the only Book preserved out of other Divine Books in real words. We take honor in the effort we put with our kids to memorize the while Quran by heart one generation after another.

 

2- Judge the Book by what is written in it. Let him study the Quran in a genuine approach not already self-determined to have pre-judgements on it.

 

The Quran speaks of law, ethics, history, language and much more. Have him study it like any academic researcher and see what he concludes out of that.

 

Almighty Allah knows best.