Derasha 621 on Mishpatim 24:16

English: Reish Lakish said to Rabbi Yochanan: From where do we derive the requirement of separation before entering the Divine camp? From Sinai, as it says, “And the glory of the LORD rested upon Mount Sinai, and the cloud covered it six days, and He called to Moshe on the seventh day.” Since the verse already says that He called to Moshe on the seventh day, why mention the six days? This establishes a principle: anyone entering the camp of the Divine Presence requires six days of separation beforehand.