One of the long-standing objections levelled against the Qur'ān by its non-Muslim critics is that it appears to have no regular form or structure. It is said that its verses follow one another with little sense of interconnection and its sūrahs seem to have been arranged in a sequence based on the crude principle of diminishing length, the longest coming first and the shortest going to the end. Almost every sūrah, it is complained, is riddled with unsettling shifts of scene, address, and subject and one cannot with any amount of certainty predict what is going to come next. It is concluded that the Qur'ān is, at best, a remarkable compilation of unrelated passages, or a book of quotations. That though it is full of pearls, the pearls are lying in a promiscuous heap.
The actual words used by those who have raised this objection are much more stern and caustic. We will not quote them, partly because they may be found in any book written on the Qur'ān by any critic of Islam and partly because their pungency does not add to the gravity of the objection. We shall only note that new as well as old orientalists have made the point often and that for all the difference in their approaches to the Qur'ān, they are all agreed that the Qur'ān completely lacks anything of the kind of orderly arrangement. Some of them have actually tried to rearrange the Qur'ān either chronologically or according to some other self-devised principle.
The response of Muslim scholars to this objection has been, generally, concessive. They grant that the Qur'ān does not have the arrangement of a well-planned book, but then, they say, it was never meant to have one. The revelation of the Qur'ān, they point out, was completed in twenty-three years and during that period the Qur'ān dwelt on such a large number of diverse subjects that no act of compilation could have given it greater unity and coherence than that it now possesses. The Qur'ān, they say, dealt with the lives, activities, and problems of a whole nation for a long span of time and so any objection based on the concept of a research thesis is bound to be misplaced. Read the rest here.