Why did Moshe repeat "Va'esnapal... Arba'im Yom
Rashi: In order to add the basic text of his Tefilah, which the Pasuk goes on to quote. 1
Rashbam: He repeated it here as part of the rebuke. He pointed out to the people that he succeeded in preventing their immediate annihilation due to Chilul Hashem, to prevent people from saying that Hashem was incapable of conquering the Cana'anim. After they enter Eretz Cana'an and defeat the Cana'anim however, this will no longer apply, so if they sin then, nothing will prevent Hashem from destroying them. 2
It teaches that also for these other Aveiros, Moshe needed to pray for them for forty days. Refer to 9:22:2:3 and the note there.