Peter J. Gentry has an article dealing with how and why the present shape of the Old Testament exists. The article is fairly comprehensive and technical but very readable for any layperson familiar with the bible. One does not need to analyze all his technical charts he presents, from himself or others, to fully grasp the points he is making. He writes in a very straightforward manner. I believe the article has great explanatory power and have benefitted from it probably more than any other work on this topic either in writing or speech. He says just enough in 20 pages along with about 7 pages of footnotes.