What was the significance of Moshe's (third) stay on Har Sinai?
Rashi: It was to receive the second pair of Luchos; and the Torah mentions it here to teach us how long he remained there. 1
Da'as Zekenim, Hadar Zekenim and Rosh: It was to receive the second Luchos and to Daven for a total pardon for Yisrael.
Oznayim la'Torah: Even though Hashem pardoned Yisrael for the sin of the Eigel following Moshe's second set of forty days on Har Sinai, 2 the danger remained, since Hashem said that He would send a Mal'ach to replace Him - an agent who did not have the power to forgive them should they sin. And that is what Moshe achieved during his third set of forty days - when Hashem now told him to lead the people - under the direct supervision of Hashem - and not a Mal'ach.
What are the implications of the words "ka'Yamim ha'Rishonim"?
Rashi: It implies that these forty days were days of goodwill, just as the first ones were 1 - as opposed to the middle forty days when Hashem was angry.
Ramban (citing the Seider Olam): To teach us that, during these forty days, Moshe Davened to Hashem with the thirteen Midos ('Hashem Hashem?') just as he did during the first forty days. 2
Sifsei Chachamim: The first days, before Chet ha'Egel, were of total good will; the last days were not, for Hashem said "Salachti ki'Dvarecha" only at the end, on Yom Kipur. They are compared to the first days to teach that we do not discuss the middle days.
Ramban: And just as He did the first time, Hashem answered Moshe positively, as the next Pasuk explains.
What are the implications of "Lo Avah Hashem Hashchisecha"?
Ramban #1: It implies that Hashem did not want you to lose coming to Eretz Yisrael and inheriting it. 1
Ramban #2 (according to Kabalah): It implies that Hashem will not banish from His great Name, inasmuch as it will not accompany you. 2
Ramban: We find that 'Hashchasah' has this meaning so in Matos Bamidbar, 32:15.
See R. Chavel's notes.
