Its doctrine of revelation and its ethical model.
The Koran, while not the whole of Muslim doctrinal authority, is central to it. And Muslim doctrine about the Koran is as important as the text itself, because it tells you what it is that you are reading and how to read and interpret it. And Muslim doctrine about the Koran is that it is the dictation –the word-for-word copying– of what the Angel Gabriel told Mohammed. So there was no human ingenuity or creativity synergistically involved in co-creating the text. This is Allah’s direct and, by the way, eternal Arabic message. Gabriel is his secretary and Mohammed is just repeating what the secretary told him. The Koran is not divinely inspired, but divinely and literally dictated.
Second, all of Muslim ethics, both theoretical and practical and legal, centers on copying what Mohammed did. The voluminous Hadith and the classic biographies of the prophet provide vast amounts of detail –through asserted chains of oral tradition– about his doings and saying, all of which become literal models for Muslim behavior. Muslim ethics and law –and it is a religion of law above all, like its elder Semitic sister, Judaism– is about copying.
So, simply, put if your model of revelation is dictation and your model of ethics is copying, don’t expect too much creativity.