What is the significance of the "Af va'Cheimah"?
Ramban: Despite the fact that Hashem had already retracted from His initial threat to wipe out K'lal Yisrael, 1 Moshe found it necessary to ascend Har Sinai to Daven on their behalf to protect them against the wrath and the rage of Hashem.
Targum Yonasan: When, following the sin of the Golden Calf, Hashem sent down five angels - Af, Cheimah, Ketzef, Mashchis and Charon - to destroy Yisrael, Moshe roused the Avos from their graves to Daven for them. They succeeded in eliminating the latter three, and now, with his Tefilos, Moshe eliminated Af and Cheimah. 2