וַתִּקְרְב֥וּן וַתַּֽעַמְד֖וּן תַּ֣חַת הָהָ֑ר וְהָהָ֞ר בֹּעֵ֤ר בָּאֵשׁ֙ עַד־לֵ֣ב הַשָּׁמַ֔יִם חֹ֖שֶׁךְ עָנָ֥ן וַעֲרָפֶֽל׃
Und ihr kam näher und stand unter dem Berg; und der Berg brannte mit Feuer bis ins Herz des Himmels, mit Dunkelheit, Wolke und dicker Dunkelheit.
Zohar
R' Yitzḥak says: Why was the Torah given in fire and darkness? As it is written (Devarim 4:11) "The mountain was ablaze with flames to the very skies, dark with densest clouds." The reason is because every person who toils in Torah is saved from the fire of Gehinom, and from the darkness with which the other nations darken Israel, since the merits of Avraham save Israel from the fire of Gehinom.
Zohar
"Without form" means strangulation, as it is written, "a line of confusion" (Isaiah 34:11) that is "a measuring line" (Zech. 2:5). "Void" means stoning and refers to the stones that are sunk in the great deep for the purpose of punishing the wicked. And "darkness" means burning. As it is written, "And it came to pass, when you heard the voice out of the midst of the darkness, while the mountain did burn with fire" (Deut. 5:20). And this fierce fire "shall fall upon the head of the wicked" (Jer. 23:19) to burn them.