Muhammed was illiterate. He had friends who could read, but he himself could not. So in the original story God dictated the Koran to him, and he recited it to his friend who wrote it down. The more you think about this the less it makes sense.
As such the Koran is supposed to be the literal word of God. I mean, it clearly isn't, because even if you accept that there might be a deity, the book itself is very poorly written. It's very obviously a product of the minds of the time, and you don't need a language degree to see that.
This finding is a huge problem for people who believe that the Koran is the literal word of God, dictated to Muhammed. Unlike the Bible, where it is accepted that there are many authors and many of them were not alive at the time of the events depicted, and each had their own agendas etc, the Koran is supposed to be perfect. Any flaw would be a flaw in God's work.