Rashi on Exodus 19:9/רש"י על שמות י״ט:ט׳

1בעב הענן signifies in the thickness of the cloud, and this is the ערפל, the thick darkness mentioned in Exodus 20:18 “And Moses stepped near unto the thick darkness where God was” (Mekhilta).

2וגם בך AND IN THEE ALSO [WILL THEY BELIEVE] — The word “also” implies that they will believe also in the prophets who will come after thee (Mekhilta).

3ויגד משה את דברי וגו׳ AND MOSES TOLD THE WORDS OF [THE PEOPLE UNTO THE LORD] on the following day which was the fourth of the month.

4את דברי העם וגו׳ THE WORDS OF THE PEOPLE etc. — He said to God: “I have heard from them a reply to this statement — that their desire is to hear the commandments from You and not from me. One who hears from the mouth of a messenger is not the same (in the same position) as one who hears directly from the mouth of the King himself. It is our wish to see our King (cf. Mekhilta).