Why does the Torah insert this Pasuk?
Rashbam: To teach us why the people were afraid, as an introduction to 5:22 - where it tells us what they said to Moshe in their state of fear and what Moshe answered them.
How will we reconcile this Pasuk with the Pasuk in Yisro, which compares the smoke on Har Sinai to the smoke of an oven?
Refer to Sh'mos. 19:11:1:1.
What is the definition of "Choshech, Anan va'Arafel"?
Rashi (in Yisro, Sh'mos, 20:18), Targum Onkelos and Targum Yonasan: They refer to the three levels of darkness
What is the significance of the three layers of darkness?
Oznayim la'Torah: All of Yisrael reached a level of prophecy at Matan Torah. However, they were not on the level of Moshe, the Master Navi, who saw the Shechinah with Aspaklarya ha'Me'irah (a clear vision) , where Hashem, who was visible (Kevayachol), was covered only by the Anan, 1 as opposed to Yisrael, who only saw the Shechinah with Aspaklarya she'Einah Me'irah, where Hashem was covered by the Anan and hidden behind the Arafel. 2