Devarim II - Did Moshe compose it?

There are basically two ways of understanding the authorship of Devarim. The first is simply that G-d composed it just as He composed the other four books of the Torah. There is an alternative view that in fact Moshe composed Devarim. Below are examples of the two views.

Devarim composed by G-d

Chinuch(Introduction to Devarim before #414): The Ramban wrote in his introduction to Devarim that the nature of Devarim is well know – it is a restatement of the Torah. In it Moshe reviewed to the generation, that was about to enter Israel, most of the mitzvos that they would need to know to settle the Israel. He commands many mitzvos and threatens them strongly concerning the punishment for not keeping the commandments. Occasionally he adds explanations to some of these mitzvos. However he makes no mention of mitzvos which applied to the Cohanim. Furthermore he doesn’t add to the commandments of the Cohanim since they were highly motivated to keep their mitzvos (Shabbos 20a). Moshe also adds mitzvos in Devarim which have not been mentioned previously at all such as Yibum (levirate marriage), slandering one’s bride, divorce, scheming witnesses and others. There is no doubt that these were not new mitzvos but those which had already been told to Moshe at Sinai or in the Tent of Meeting (Ohel Mo’ed) in the first year. That is because on the Plains of Moav there were no new revelations of mitzvos except for the words of the Covenant as will be explained [Devarim 28:69]. Since there were no new mitzvos revealed by G‑d for the first time here – you don’t find in Devarim the expression “And G‑d spoke to Moshe saying, ‘Command the Jews’ or ‘Speak to the Jews and you say to them this mitzva’. These are the words of the Ramban. This that these mitzvos were not mentioned previously with the other mitzvos is not surprising. That is because our Sages say in many places [Pesachim 6b] the Torah is not presented in chronological order. The reason for this is that the Torah includes all wisdoms aside from the plain meaning of the verses of its sweet issues and the strong foundations of its mitzvos. Perhaps because of the concealed wisdom it had to be arranged in the pattern that we have. Thus all is precisely placed by the Master of Divine Wisdom and that is sufficient justification.

Devarm composed by Moshe

Ohr HaChaim(Devarim 1:1): These are the words that Moshe spoke to the entire nation… By saying “these are the words” it comes to exclude what was written previously in the Torah. In other words Devarim consists entirely of the words which Moshe spoke on his own initiative i.e., the chastisements and instructions to those who transgress G‑d words. Megila (31b) states the curses which are mentioned in Devarim were composed by Moshe. However even the laws which Moshe reviewed and explained, he did on his own initiative without a command from G‑d. Since Moshe composed the Book of Devarim, the Torah was concerned that we might mistakenly think that he might have also independently composed part of the previous four books of the Torah. That is why Devarim starts with “These are the words that Moshe spoke” - to tell you that only the words found in Devarim were Moshe’s own composition but not even a single letter of the Torah that preceded it. Those four books of the Torah were entirely from G‑d exactly as He commanded them without the slightest change – even a single extra letter added or subtracted.