Rashi on Exodus
בעבר כבדי WHEN MY GLORY PASSETH BY – i. e. when I shall pass before you.
Siftei Chakhamim
When I pass by you. [Rashi is explaining that] “My Glory” refers to God Himself. The proof is that afterward it is written, “Until I pass by,” rather than, “Until My Glory passes by.”
Daat Zkenim on Exodus
והיה בעבור כבודי, “it will be when one of My attributes passes;” I am placing you into the cleft in the rock in order that you will not need to look at My essence with your face (to protect you) ושכותי כפי, “I will cover you with the palm of My right hand;” this is a simile for a cloud G–d will place between Himself and Moses. We find a similar expression in Lamentations 3,41:נשא לבבינו אל כפים אל אל בשמים, “let us lift up our hearts with our hands to G–d in heaven.” In other words: “I will act as a protective cloud in front of you to prevent you from seeing ‘Me’ with your eyes.