He Lifted the Mountain Over Them for Their Benefit:
The Gemara says (Shabbos 88A) that as the nation stood by the mountain, Hashem lifted it over their heads like a barrel and said, “If you accept the Torah, that is fine and good, but if you do not then you will be buried here.”
The Chida (Sefer Pnei Dovid) says that since Hashem forced us to accept the Torah, He can never send us away. He compares this to the halacha that says that if a man forces himself onto a woman, he must marry her and can never send her away (Devarim 22:29). He says that the pasuk can be read to be saying that “they stood”, meaning that Klal Yisroel will stand for all time, because we were “at the bottom of the mountain”, because the mountain was placed over us and we were forced to accept the Torah. According to this explanation, it was a great favor for us for Hashem to hold the mountain over our heads.
Accordingly, he explains that after Moshe Rabenu hinted to the sins of Klal Yisroel, he told them that Hashem spoke to them “at Chorev”, meaning that He spoke to them when he lifted the mountain above their heads and said that they had “dwelt enough on this mountain” to be assured that they would never be sent away, no matter how many sins they commit.
