Progression is holiness. God emphasises how holy he is by having layers, like the temple would be with its holy of holies. It has an outer court for gentiles, a court for women, etc.
A sacrifice is offered, blood sprinkled, then a group leave the people and go further up the mountain. Finally, Moses takes the last bit solo.
The natural display, cloud, fire etc envelopes Moses. The stage is set for more revelations.