Why does Moshe repeat "Va'esnapal... Arba'im Yom
Rashi: In order to add the basic text of his Tefilah there, 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, lest people say that Hashem was incapable of conquering the Kena'anim. After they enter Eretz Kena'an and defeat the Kena'anim, this will not 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 40 days. Refer to 9:22:2:3 and the note there.