G-d is giving a personal care for Moshe upon him leaving the world. As we know from the Zohar, Moshe was at the level of Daat (the connection Sefirah of Chokmah and Binah). It is above the physical level. In Deuteronomy 31:2, Moshe is telling the Israelites " And he said unto them: \’I am a hundred and twenty years old this day; I can not go out and come in anymore; " in his preparation to transfer the leadership to Joshua . Go out and come in refers to the traveling from the physical to the spiritual in order to talk to G-d. No one could see G-d and live because to see G-d you need to be spiritual. Moshe could transform himself to go between the two dimensions.