וַיֹּ֨אמֶר יְהוָ֜ה אֶל־מֹשֶׁ֗ה הִנֵּ֨ה אָנֹכִ֜י בָּ֣א אֵלֶיךָ֮ בְּעַ֣ב הֶֽעָנָן֒ בַּעֲב֞וּר יִשְׁמַ֤ע הָעָם֙ בְּדַבְּרִ֣י עִמָּ֔ךְ וְגַם־בְּךָ֖ יַאֲמִ֣ינוּ לְעוֹלָ֑ם וַיַּגֵּ֥ד מֹשֶׁ֛ה אֶת־דִּבְרֵ֥י הָעָ֖ם אֶל־יְהוָֽה׃
И сказал Господь Моисею: 'Вот, я приду к тебе в густом облаке, чтобы люди услышали, когда я говорю с тобою, и также могли бы поверить тебе вовеки.' И сказал Моисей слова народа Господу.
Rashi
בעב 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).
Chizkuni
ויגד משה, Moses told G-d what the people had said in detail. When we encountered a similar phrase previously in verse 8, it was appropriate for the Torah to use the expression: וישב, “he brought back a reply,” as at that point he brought back a reply to something that had been requested from them, i.e. “if you will surely listen to Me.” Now there was no need to phrase their comments in this mode, as their willingness to obey G-d’s wishes had been established already. As Rashi noted, “It is our wish to see our King.”
Ramban
IN A THICK CLOUD. This is the thick darkness where G-d was,187Further, 20:18. and all the people saw it and recognized it as such, as it is said, And the appearance of the Glory of the Eternal was like devouring fire on the top of the mount in the eyes of the children of Israel.188Ibid., 24:17.