וַיִּשְׁכֹּ֤ן כְּבוֹד־יְהוָה֙ עַל־הַ֣ר סִינַ֔י וַיְכַסֵּ֥הוּ הֶעָנָ֖ן שֵׁ֣שֶׁת יָמִ֑ים וַיִּקְרָ֧א אֶל־מֹשֶׁ֛ה בַּיּ֥וֹם הַשְּׁבִיעִ֖י מִתּ֥וֹךְ הֶעָנָֽן׃
And the glory of the LORD abode upon mount Sinai, and the cloud covered it six days; and the seventh day He called unto Moses out of the midst of the cloud.
Read kabbalistic (mystical) interpretation of Exodus 24:16: and classical mystical sources.