When Moses asked who was he to lead God’s people at the burning bush, wondering about his qualifications, the Lord replied that he would be with him. The sign of this, would be a return with the people to serve God on the mountain. In Exodus 19 it has come to pass.
What happens in Exodus 19 is that Moses runs up and down the mountain. In verse 3 he goes up to God, and the Lord speaks to him, offering a covenant to the people. So Moses goes down, in verse 7, and he tells them what God is proposing. The people accept, and, as we see in verse 8, Moses goes back to tell the Lord what the people have agreed. Then the Lord gives Moses instruction on how they are to prepare for the encounter. In verse 14 it tells us that Moses again goes down and instructs the people as he has been told to do by the Lord.
The coming of God is with cloud and majesty and awe. There is deafening noise, lighting and smoke, and a tremendous earthquake. The people approach, and once again Moses is called up to the top of the mountain. There, God again tells him to go down and make sure nobody comes uninvited. At this point a beleaguered Moses pushes back in verse 23. Bounds have been set, nobody is about to approach. Haven’t we been through all this already?
The Lord brusquely tells him to quit arguing and get going, in verse 24; and so Moses does. He reinforces the restrictions and is told to fetch Aaron, the designated priest. There was probably an informal priesthood in Israel, as in most every other place, but God wants to impress on them how he will regulate that core aspect of the covenant he makes. The back and forth is dragged out longer. As the people wait, Moses descends once more.
The point of all this is that Moses is the go-between. He is the mediator of the old covenant: one who goes up to God because God calls him, who is sent to the people, gets their consent, relays it back to God who knows what is in each person’s heart and has no need for any man to tell him anything but still requires Moses to do so anyway. When all things have been accomplished, the last clause about a priesthood is added, prolonging the delay and adding an extra descent and ascent of the mountain for this hard working 80-year-old man (who was also terrified).
There is one who comes down from heaven and returns there without running up and down the mountain. There is a better covenant, and there is a better mediator. The temporality of the old covenant and its outward nature is seen in the natural phenomena the angelic presences that mediated it worked, and in the constant ascending and descending required of the man Moses. There is a better mountain, and that is the mountain of the Lord, Zion, which is the place where Jesus Christ is, who has come down and who raises his people up, and whose priesthood is superior. There is a greater need to listen than in that moment back at Sinai when the terrified people heard God speak at last.
Heb 12:18–24 For you have not come to the mountain that may be touched and that burned with fire, and to blackness and darkness and tempest, 19 and the sound of a trumpet and the voice of words, so that those who heard it begged that the word should not be spoken to them anymore. 20 (For they could not endure what was commanded: “And if so much as a beast touches the mountain, it shall be stoned or shot with an arrow.” 21 And so terrifying was the sight that Moses said, “I am exceedingly afraid and trembling.”)
22 But you have come to Mount Zion and to the city of the living God, the heavenly Jerusalem, to an innumerable company of angels, 23 to the general assembly and church of the firstborn who are registered in heaven, to God the Judge of all, to the spirits of just men made perfect, 24 to Jesus the Mediator of the new covenant, and to the blood of sprinkling that speaks better things than that of Abel.