Islam is the last phase of The Divine Religion.
Accordingly, Quraan is the Last Testament and Mohammad is the last of the Abraham family of prophets. He is the grandson of Ishmael and the cousin of Moses and Jesus.
Since Quraan is the last Divine Book it had to be preserved in a way that would guarantee its integrity till the end of time. For this purpose God chose to reveal it in the Arabic language thus making it "Quraan's time capsule".
The Arabs were linguistic fanatics; they used to have their own Olympics in the different Arabic language competitions such as poetry, story telling, memorization and grammar. They used to have an annual gathering in Mecca around the Kaaba (The Holy House) and the winning works would be hung on the Kaaba's drapes.
The fact that most of the Arabs were illiterates didn't stop them from enjoying these events because most of the events were verbal and the Arabs had an amazing ability of memorization.
Among those people the Quraan was revealed in a perfect Arabic tongue presenting a miraculous challenge to those linguistics which forced most of them to embrace Islam. "There is no way that Quraan is written by a man", they all agreed.
Those early Muslims had the ability to memorize Quraan as it was revealed when it was revealed.
When the revelation stopped, there were thousands of Muslims who memorize all of the Quraan which is now printed in 600 pages. Of the approximate 1.2 Billion Muslims living nowadays it is estimated that 5 – 6 Million of them memorize the Quraan in its entirety. In Arabic the words meaning "Quraan Memorizer" conveniently mean "Quraan Keeper".
Quraan was not compiled in one book in the living days of the Prophet Mohammad pbuh nor in the days of his first successor Abu Bakr.
It was Omar, the second successor about 15 years after the death of the Prophet who decided to start writing down the Quraan in one book because a lot of the Quraan Keepers were either killed in battles or dying of old age. This task was completed many years later in the days of the third successor Usman.
In order for one phrase to be written down in the Book, at least two Quraan Keepers must have approved it.
Although the Quraan is in the Arabic language, not all of it is understood. Not now and not when it was revealed more than 14 centuries ago. The Prophet Muhammad pbuh explained some of it but he left a lot of it without explanation. In its text God makes it clear how it was revealed in different types of verses and that only He knows all of its interpretation. Islam rules and commands are clearly revealed and understood. Muslims are required to follow these rules and commands. Quraan keeps on revealing its secrets as time goes by. Nowadays Muslims understand much more than early Muslims did. Another proof that Islam is good for all places and all times.
Therefore God has ordered Muslims to only read it. Reading the Quraan gives knowledge to the reader. Also the Quraan has healing powers. In it lies the original program of the human being. Reading the Quraan frequently and finishing it repeatedly in 30 days periods cures any physical and mental illnesses and raises one's immunity levels against natural and supernatural threats.
Non-Arab Muslims understood this and applied it to themselves. In countries like India, Pakistan, Afghanistan and other non-Arabic speaking Muslim countries there are a lot of people who perfectly memorize parts or all of the Quraan in the perfect Arabic language without speaking it or even understanding the meaning of what they memorize.
Even translated Quraan has some of these miraculous powers. I’ve personally met people who found God on their own only by reading the English translations of the Quraan, a practical implementation to what God said in it about it: “Guides to the truth”.