Often times my question "How do you know the Qur'an is from God?" is met by Muslims with a response like this: No disrespect intended but I really do not see how you can make a stronger claim for the Bible to be a book of God. ... On the other hand, there is no debate or doubt as to whether the Qur'an that we have today is the same as was revealed to the Prophet Muhammad (or if there is it is minimal). The whole tradition in which the Qur'an was compiled as compared to the Bible would make it a more accurate historical/religious text.
This obviously completely misses the mark and does not answer at all the question I posed. It confuses the following two questions:
1. Is the text of the Qur'an accurately preserved?
2. Is the Qur'an true? Is the Qur'an from God?
In addition, those two questions are logically independent. The answer to the first question will tell me nothing about the answer to the second question. Let me illustrate this with an example.
There is a movement that is denying that the Holocaust [the murder of 6 million Jews in Nazi Germany] has ever happened. Those people write books and distribute them. Those books are available in libraries, for example, the library of congress, the British Library, and other libraries, which stock basically all books ever published.
In 200 years, [if judgment day has not come by then] these books will still be the same. They will still be accurately preserved. However, obviously their content will be just as wrong as when it was first written and accurate preservation does not make it any truer.
If the Qur'an was not originally from God, then all the most accurate preservation will not make it into the word of God. That is what my question was about. How do we know that the Qur'an was from God in the first place?
The preservation question will never answer the truth question.
To extend the illustration, let us look at the normal process about most university textbooks that go through several editions. The first edition might still have some inaccuracies; it is not dealing exhaustively with some topics, which should be included. Nevertheless, it is a successful textbook. Soon a reprint is necessary. There is no time to change all that should be changed. However, the author makes sure that the so far discovered misprints are corrected. For the next print run, he reworks some of the topics where inaccuracies have been found and corrects mistakes of content as well as further misprints that were pointed out to him. For the third print a major overhaul is done, a new chapter on a topic so far omitted is added, more inaccuracies are corrected as well as more of the misprints reported up to date.
In the first illustration, we have seen that completely accurate preservation does not not imply truth. In this illustration, we see that change of the text can actually improve truth and make something true, which was wrong before.
Both examples together should make it completely clear that the issue of preservation will never give us an answer to the question whether the content of the book is true.
To add a last thought, if a book is totally true in the beginning is then through many stages of copying by hand has undergone slight changes because it is impossible not to make mistakes when copying by hand, but apart from these scribal errors it is basically the same as the original, then obviously this book will still be true.
Preservation questions are important, but they will never answer the question of truth. For both the Bible and the Qur'an we can show that there are textual variations as they come with any book that is copied by hand for centuries. For both the Bible and the Qur'an we can show that they are essentially the same today as they were in the second and 8th century respectively. We can indeed have the confidence that both texts accurately represent what was the original.