Moses was a great and powerful servant of Yahweh.  He knew that the task of leading the people of Yahweh was difficult.  Moses told Yahweh that he could not do it without his help. Moses needed the assurance that Yahweh would be there for him during the wilderness journey.  Yahweh gave Moses the encouragement that he needed to sustain him.  Moses wanted to see the Face (Heb. Faces) of Yahweh.  Yahweh told Moses that no man could see his "Faces" and live.  Moses, however, got to both see the backside of Yahweh and hear Him preach!