On the morning of the third day, as the eyes of all the people were turned toward the mount, its summit was covered with a thick cloud, which grew more black and dense, sweeping downward until the entire mountain was wrapped in darkness and awful mystery. Then a sound as of a trumpet was heard, summoning the people to meet with God; and Moses led them forth to the base of the mountain. From the thick darkness flashed vivid lightnings, while peals of thunder echoed and re-echoed among the surrounding heights. “And Mount Sinai was altogether on a smoke, because the Lord descended upon it in fire: and the smoke thereof ascended as the smoke of a furnace, and the whole mount quaked greatly.” “The glory of the Lord was like devouring fire on the top of the mount” in the sight of the assembled multitude. And “the voice of the trumpet sounded long, and waxed louder and louder.” So terrible were the tokens of Jehovah's presence that the hosts of Israel shook with fear, and fell upon their face…
"And so terrible was the sight, that Moses said, I exceedingly fear and quake:)"
Ellen White directly references Hebrews 12:21 in this passage.
"Mount Paran, and He came with ten thousands of saints: from His right hand went a fiery law for them. Yea, He loved the people; all His saints are in Thy hand: and they sat down at Thy feet; every one shall receive of Thy words.” Deuteronomy 33:2, 3 . PP 304.3"
"And he said, The Lord came from Sinai, and rose up from Seir unto them; he shined forth from mount Paran, and he came with ten thousands of saints: from his right hand went a fiery law for them."
EGW directly quotes Deuteronomy 33:2, confirming the connection.
"Yea, he loved the people; all his saints are in thy hand: and they sat down at thy feet; every one shall receive of thy words."
EGW directly quotes Deuteronomy 33:3.