In his introduction to Sefer Devorim, the Ramban writes B'lashoin Safeik whether the additional Mitzvois that are told to Klal Yisrael in Sefer Devarim were told here at the end of the 40 years in the Midbar or were they told earlier and for whatever reason they were written here. It is a Davar Pele, because the Ramban has a Tzad that perhaps all these Mitzvois were not Noiheig in the Midbar and for whatever reason the Ribboinoi Shel Oilam pushed it off until this point.
Chumash Devarim has many common Mitzvois like Kriyas Shema, Birchas Hamazon, Kiddushin, Gittin, and Yibum. In Parshas Ki Seitzei there are the rules of who a person is permitted to marry. As a matter of fact, Chumash Devarim has more Mitzvois than any of the other Chumashim. Yet the Ramban says, that these Mitzvois were said here at the end.
Interestingly, the Kli Chemda at the beginning of the Parsha brings a Teshuvas Haratbaz in Kli Chemda, Gimmel. The Ratbaz is Matmia on the Ramban. He says could it be that Moshe Rabbeinu hid his Nevua for 40 years? The Kli Chemda says this isn't such a Shtarke Kasha because the Ribboinoi Shel Oilam told him to hide it. There is a Prat that is very Shver. The Ramban says that maybe the reason why Hakadoish Baruch Hu pushed it off until here is because these Mitzvois are Mitzvois She'ainoi Tidiroi, meaning they are Mitzvois that don't come up all the time. Many of them are Noiheg only in Eretz Yisrael and it wasn't important to mention them prior to here. The problem of course is Birchas Hamazoin and Kriyas Shema that does come up all the time. Regarding Birchas Hamazoin, the Kli Chemda says something very interesting.
In Maseches Berachois 20b that was mentioned last week in connection with the Machloikes Rashi and Toisafos regarding if women are Mechuyav in Birchois Hamazoin Midioiraisa, Rashi 32 lines from the top in Dibbur Hamaschil Oi Dirabanan says that Eretz is Mi'akeiv in Birchas Hamazoin (או דרבנן. דכתיב על הארץ הטובה אשר נתן לך (שם)והארץ לא נתנה לנקבות להתחלק ואי משום בנות צלפחד חלק אביהם הם דנטלו שהיה מיוצאי מצרים). Since women don't have a Cheilik in Eretz Yisrael they wouldn't be Mechuyav Midioiraisa in Benchting. The Kli Chemda says very Geshmak, Klal Yisrael in the Midbar didn't have a Cheilek in Eretz Yisrael, so Mimeila they weren't Michuyav in Birchas Hamazoin the whole 40 years that they were in the Midbar. It fits well. The Gemara says Kisheyarad Lahem Haman Tiken Lahem Moshe Birchas Hazon. Moshe Rabbeinu made a Takana, so it is a D'rabanan that they should say the first Beracha of Benchting until Hazon Es Hakoil. The Beracha of Noide L'cha that discusses Eretz Yisrael wasn't Mesaken at that time. Moshe was Mesakein the Beracha in order for Klal Yisrael to give thanks and Hakaras Hatoiv for the Man. It is very Geshmak according to this that the Mitzvois were Einoi Tidiroi. The Gemara says that they were able to buy Chitim from the Bedouins that roamed in the Midbar so it was Einoi Tidiroi. According to this, it wasn't even Shayich to them the Mitzvah of Birchas Hamazoin and Mimeila it is Geshmak that the Mitzvah wasn't given until later.
There is a question regarding the Tefillin that they wore. The Mitzvah of Tefillin is in Parshas Bo, however, 2 of the Parshois of Tefillin (Shema and Vehoiya Im Shamoi'a) are first here in Chumash Devarim. So what type of Tefillin did they wear? Here we can't say that they weren't Mechuyav in Tefillin because they were Mitzuva in Parshas Bo. The Brisker Rav says that they had Tefillin with all 4 Parshios. However, the Parshios of Shema and Vehaya have 2 Dinnim. There is one Din that they are part of Torah meaning it didn't exist until here and the other Tzad is that it is part of Tefillin and Tefillin they received as a Mitzvah in Parshas Bo already with these 2 Parshios included.
A last question on the Ramban is that the reading of Kriyas Shema since it is done daily how could the Ramban say that the Mitzvois listed in Chumash Devarim are Mitzvois that are Einoi Tidiroi?
Kim'at the last Shiur that I heard from Rav Moshe was when the Yeshiva had just started learning Maseches Gittin. Rav Moshe mentioned that the first Toisafos in Gittin which is Dibbur Hamaschil Hameivi Get (המביא גט. אע"ג דלשאר שטרות פעמים נמי קרי גט כדתנן בהשולח (לקמן דף לד:) אין עדים חותמין על הגט אלא מפני תיקון העולם ואיירי בכל שטרות ובפרק התקבל (לקמן דף סד.) נמי תניא וכן לגיטין ומפרש התם גיטי ממון מ"מ לא הוצרך לפרש כאן גט אשה משום דברוב מקומות היכא דקתני גט סתם איירי בגט אשה ומה שנוהגים לכתוב י"ב שורות בגט אומר ר"ת משום דגט גימטריא י"ב ור"י שמע בשם רב האי גאון ובשם רבינו סעדיה משום דכתיב ספר כריתות כשיעור י"ב שיטין המפסיקין בין ארבעה חומשי ספר תורה כדאמר בבבא בתרא (דף יג:) שצריך להניח ארבעה שיטין בין כל ספר וספר והפסק שבין וידבר למשנה תורה לא חשיב שאינו אלא חוזר ושונה מה שלמעלה) explains that the reason why a Get has 12 lines is Merumez to the blank lines between the Chumashim in a Torah. Between every Chumash is 4 blank lines which is = to 12 lines (between Beraishis and Shemos (4), between Shemos and Vayikra (4), and between Vayikra and Bamidbar (4)). What about the 4 blank lines between Bamidbar and Devarim? Toisafos says 3 lines before the end of that Toisafos, V'hefseik Shebain Vayidabeir L'mishne Torah, Loi Chashiv, She'einoi Ela Choizer V'shoine Ma Shelamala. Meaning there is nothing new in Devarim and it is only Chazarah from what was mentioned earlier. Rav Moshe asked, there are more Mitzvois in Devarim than in any other Chumash?
Rav Moshe answered if Klal Yisrael had not been in the Midbar for 40 years there would not be a Chumash Devarim. However, where would these Mitzvois be? There are Parshiyois in the Torah that are full of the Chataim of Klal Yisrael. For example, Ki Sisa - Eigel, Shelach - Meraglim, Koirach. Had it not been for the Chataim, the MItzvois would have been there. Like this the Torah would have been complete after only 4 Sefarim.
