Why does the Torah repeat the requirement to distance the nation from the mountain? Is this the first arrival of Bnei Yisrael at Sinai, or had they been there before, in the story of Massa u-Meriva? Why does the Torah parallel God's revelation at Sinai with the nation's previous request for water?

Courtesy of the Virtual Beit Midrash, Yeshivat Har Etzion