In other words the Quran is not a visual miracle but it is an audio miracle. With all God's great prophet they are equip with a miracle so that they may convince sceptic. Here there is a lesson to be learnt, when you perform God's work he will supply you with the necessary tools to get the job done. Musa can turn his stick into a snake and part ocean with it.
Isa can bring the dead to life and cure incurable illnesses. Some might say it is not fair all the other prophet got these cool stuff and all Muhammad gets is just a book. Well it is not just any book, it is the book that contain a linguistic miracle.
Many people who are against Islam change their minds when they read the Quran. You do not have to go to the early days of Islam where its enemies embrace Islam in droves after listening to the Quran. Remember the Minaret ban in Switzerland. The politician who is behind it, Daniel Streich embraces Islam after he bought a Quran with the intention to find weakness in it and attack Islam.
Many have taken the challlenge, but none from the time of Muhamad till this very day. All the great minds in this world from the year 300 century till now can't even match three sentences of the Quran. So what is so great about the quran? Brother Nouman Khan explains it in a simplistic manner.