Book of Deuteronomy have given various answers to the problem. The Deuteronomistic history theory is currently the most popular (Deuteronomy was originally just the law code and covenant, written to cement the religious reforms of Josiah, and later expanded to stand as the introduction to the full history); but there is an older theory which sees Deuteronomy as belonging to Numbers, and Joshua as a sort of supplement to it. This idea still has supporters, but the mainstream understanding is that Deuteronomy, after becoming the introduction to the history, was later detached from it and included with Genesis-Exodus-Leviticus-Numbers because it already had Moses
Leviticus Rabbah 23, 31-34, 36, 37). In this, Leviticus Rabbah differs from the Pesikta, for in the Pesikta the individual explanations are seldom lacking. And while the Pesikta rarely quotes lengthy homiletic excerpts after the proems, Leviticus Rabbah quotes such materials after the conclusion of a proem, in the course of each chapter, and even toward the end of a chapter. These excerpts have often very slight reference to the context. But otherwise Leviticus Rabbah carefully follows the form of the Pesikta. The end of each chapter in Leviticus Rabbah, like the Pesikta, consists of a passage containing a Messianic prophecy. The