וַהֲסִרֹתִי֙ אֶת־כַּפִּ֔י וְרָאִ֖יתָ אֶת־אֲחֹרָ֑י וּפָנַ֖י לֹ֥א יֵרָאֽוּ׃ (ס)
손을 거두리니 네가 내 등을 볼 것이요 얼굴은 보지 못하리라
Rashi
והסרתי את כפי AND I WILL REMOVE MY HAND — The Targum renders this by ואעדי ית דברת יקרי “I will remove the guidance of My Glory”; it means: when I shall remove the guidance of My Glory from before thine eyes — to go right away from that place,
Bekhor Shor
"I shall remove My palm and you shall see My back." Know that this is only a metaphor, for there is no back of the neck above, even among the angels, as it is written, (Ezek. 1:6) "each one had four faces," a face for each of the four directions, therefore, (Ezek. 1:9) "they did not turn when they moved, they went in the direction of [any of the four] faces." Furthermore, we may not speak of [God] thus, rather, it means to say "you shall see My back" like a man who sees a friend from behind, but can't really observe him.
Cassuto
And after I have passed, then I will remove my hand and you will see my back, and you shall not see my face. It is evident here that this is said metaphorically: you are only able to see my actions and recognize from them some of my attributes, but my very essence you cannot comprehend.