Before any declaration on the Islamic mission or on the Divine revelation, the Prophet established himself during the first forty years of his lifestyle among the Arabs that he was the most trustworthy(Ameen) and truthful person (Sadiq).
The authenticity of the Qur'anic text being a Divine revelation is established on that strength -- the truthfulness of the holy Prophet. Many orientalist scholars have opined that it would have been much easier in the given circumstances for the Prophet Muhammad to declare himself as God rather than establishing himself as the Prophet of God who received Divine revelations -- and that is because he was Ameen and Sadiq. He received teh Divine revelation and kept it in his heart with full trust and then gave it truthfully to the world.
I do not care what you believe but I have said all that to confirm my belief and all other Muslims's belief in this matter.
Prophet Muhammad himslef decided which verse will go in which Sura (chapter) of the Qur'an. He decided the order of the Suras. There is a great wisdom in the order of the Qur'an which is much too foreign for you to understand , so, I leave it here.
But I will say this:
(1) All basic principles, which were revealed in the early years (i.e in Makka), are placed in the last section of the Qur'an. That is section number 30, which begins with Sura number 78 and goes upto the last one, #114.
(2) The beginning of teh Qur'an has the Sura Fatiha, which is the baisc Muslim prayer that every Muslim has to recite at least 17 times (in eacah prayer of daily Salat, five times a day).
(3) The second chapter begins with a formal introduction to the Book, (i) What is in the Book (it is all truth, unadulterated truth),the word Book is meant to denote a Divine text containing laws, ethics and morals, (ii) who are its intended audience -- those who have faith in the Unseen, those who care about their relationship with their Creator/Lord/Sustainer, and those who care about the well-being of their fellow human beings. (iii) Man's beginning and end, and the stories of peoples who came before you, were guided but did not heed the guidance and were punished for that and were completely destroyed, therefore heed to this message, you are the chosen Ummah and thus you are to sustain, follow and take care of the guidance and the message by preserving it and passing it on to the generations who would come after you.
And then the rest of the book contains similar things. There is accompanying material in teh Hadeeth which gives further details on the past events and the future to come.
The Shi'ite (wrong)belief in the matter of things missing from the Qur'an has been discredited by teh Shi'ite authors of the commentaries on teh Qur'an, not once but many times over the generations -- that is all crap.
Both Shi'ite scholars, Ayatullah Khoie, as well as the Ayatullah Khumaynie have asserted unequivocally that the Qur'an we have in our possession today, that is kept between the two covers is both complete and totally unadulterated. It is the Qur'an of Muhammad which was given to us and it exists in that pristine and complete form. The rightful Shi'ite scholars of the earliest times, such as Shaikh Sadooq (d.991 AD / 380 A.H.). aso known as Ibn Babaway, have said the same thing.
Both The same thing has been asserted by John BUrton , independentally in his book:
The Collection of the Qur'an
Cambridge University Press (1979)
This book is available from Amazon for a very reasonable price Get it and read it. It will enlighten you.
All the stories such as Abu Bakr giving it to his daughter and then Umar giving it his are all fabrications by the misguided scholars of the third century period.
The Prophet prepared nearly five hundred of his companions who preserved the Quranic text to their memories and kept a cross check for its accuracy among themselves. There was not a single person who would recite the Quran in public and then if he misquoted , he would be immediately corrected by some one. Those reciters were known as the QURRA.
It is true that the very early version of the written text did not include any diacritical marks, since it was being read by the Arabs themselves, they knew how to read each and every word of the Qura'n. As Islam spread to other lands where Arabic was not the main language, diacritical marks were introduced in the text , so that the correct recital and the meanings would be preserved.
The other very striking feature of the Quranic text is its amazing use for a very limited vocabulary of the Arabic language. Arabic language works on a root system, nearly 99% of the words are derived from a three-letter root (sometimes four and occasionally five). By one estimate, the language has nearly 80,000 such root words. A whole family of words are created out of a single root. Only 1,560 root-words have been used in the Qur'anic text. Other than that, there are nearly 1,500 non-root words. Compare that with a good standard English dictionary, which contains some thing like 250,000 words.
The entire Qur'anic text consists of less than 80,000 words.
Qur'an is the only religious book which has existed in its original language for 1400 years.