Exodus 20:19שמות כ׳:י״ט
And the Lord said to Moshe, Thus thou shalt say to the children of Yisra᾽el, You have seen that I have talked with you from heaven.
Mekhilta DeRabbi Yishmael 20:18:2מכילתא דרבי ישמעאל כ׳:י״ח:ב׳
(Ibid.) "And Moses entered into the mist": This (his closeness to the L rd) was a function of his humility, viz. (Numbers 12:3) "And the man Moses was extremely humble, etc." Scripture hereby apprises us that if one is (truly) humble, in the end, he will cause the Shechinah to repose upon a man upon the earth, viz. (Isaiah 57:15) "For thus said the High and Exalted, who abides forever and whose name is holy (… I dwell with the oppressed and with the lowly of spirit, etc."), and (Ibid. 61:1) "The spirit of the L rd G d is upon me, for the L rd has anointed me to bring tidings to the humble, etc.", and (Ibid. 66;2) "And all of these things My hand created (… but it is to this that I look, to the poor and broken-spirited, etc."), and (Psalms 51:19) "The sacrifices of G d are a broken spirit. A heart broken and oppressed, G d will not despise." And all who are haughty of heart cause the land to be defiled and the Shechinah to depart, as it is written (Ibid. 101:5) "The haughty of eyes and the broad of heart, him will I not abide." And all the haughty of heart are called "abomination," as it is written (Mishlei 16:5) "The abomination of the L rd are all the haughty of heart." And idolatry is called "abomination," as it is written (Devarim 7:26) "And you shall not bring an abomination into your house." Just as idolatry defiles the land and causes the Shechinah to depart, so do all the haughty of heart. "And Moses entered into the mist": within the three partitions: darkness, cloud, and mist. Darkness, the outermost; cloud, within; mist, the innermost. As it is written "And Moses entered into the mist, where G d was.
Bereishit Rabbah 89:4בראשית רבה פ״ט:ד׳
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Deuteronomy 4:11דברים ד׳:י״א
You came forward and stood at the foot of the mountain. The mountain was ablaze with flames to the very skies, dark with densest clouds.