In this chapter, the elders and the people agree to abide by the LORD's covenant.
The LORD's speech finally ends, and we're ready to begin the covenantal ceremonies. The LORD has spelled out some of the terms of the covenant, and now the people need to agree with them. In the spirit of this, Moses tells everything to the people in verse 3 and the people accept the terms. Their declaration of obedience is auspicious, but as I said before, there are already clouds on the horizon: Moses equates their frequent rebellions against his authority as "grumblings against the LORD" (Ex 16:7). This suggests that perhaps their obedience will prove to be less than complete when it faces the challenges of time and circumstance.
Nevertheless, the people agree and Moses establishes the covenant by building an altar and sprinkling the people will blood from some sacrifices. He writes down all the words of the covenant, and then reads it to the people (written in verse 4, then read in verse 7: this is the "book of the covenant").
Before I move on, I want to make a few notes about the sprinkling of blood. This act draws allusions to a couple things we have seen before. The most notable comparison is to the Passover, which secured the homes of the Israelites by covering their doorposts and lintels with blood of ritually slain animals, as we read in Ex 12. The major theme of Exodus 12 is the concept of sacrificial atonement, that sin is transferred to the slaughtered animal and this preserves the Hebrew people. However, comparing it to the ritual slaughter here and also the killing of animals back in Genesis 15, when Abraham established his covenant with the LORD is inclining me to think that the Passover is very probably a covenantal act as well. I had discussed in some depth the connection between the Goshen Principle (protection from divine wrath) and the Israelite people's inheritance of Abraham's promise and covenant. Now we are seeing an even stronger connection between the shedding of blood and formal acceptance of divine covenants. It is plausible that this would have been true of contemporary covenants between earthly kings, but I don't have the historical records to verify that, so I will leave it as an exercise for the reader.
The next act of covenantal establishment is when the two parties share a meal with each other. We saw examples of this in Gen 31:43-55, when Jacob and Laban first establish a covenant to not harm one another, and then conclude by eating a shared meal. Another meal shared in a similar sense is Exodus 18:12, although it's harder to pinpoint a specific covenant that is established between Jethro and the Israelites. The covenantal meal here, however, is absolutely breathtaking.
In verse 10, it says that Moses and the elders saw the God of Israel. We are told that underneath his feet (implying human form?) there was a "pavement of sapphire", and again in verse 11, "they saw God". This is a very short passage (only 3 verses) and it leaves us pondering what they saw. For all of my emphasis on the manifestations of the LORD, we are not actually told the LORD's appearance in this chapter, which leaves it ambiguous. I believe we can partially answer the ambiguity by noting the word "feet", which as I said implies human form. I don't see how the people could see that the pavement is translucent "as the sky itself" unless they could see through it, i.e. it were floating in the air. I'm not sure. And lastly, we can analyze the LORD's appearance by considering his functional purpose for appearing: as the Lord and party to this covenant, a legal agreement. The LORD is clearly established in a position of power and lordship, while Israel is the dependent vassal, so his manifestation will likely be intended to imply that level of authority. Beyond that, the text does not say and I cannot speak. What they saw will remain a subject of our imagination.
At the end, the LORD declares that he will write down the commandments (possibly the ten commandments, but possibly also a reference to the whole law covering the feasts, the sabbath of the land, personal injury laws, etc). In yet another act of astonishing boldness, Moses goes up the mountain and enters the "glory of the LORD" which "was like a consuming fire on the mountain top." Moses spends 40 days there, which is reminiscent of the 40 days of rain during the great flood of Genesis 7. That Moses waited for seven days before entering the "midst of the cloud" is likely evoking the seven days of creation and the Sabbath of the seventh day. As I've said before, the number seven symbolically refers to completion. We also see this in the 70 elders of Israel (multiplying 7 by 10, both numbers that signify completion or fullness).
This is Moses's second major convocation with the LORD on Mount Sinai. In the first one, which we have just read, Moses was given a set of religious and moral commands, some embellishments on those commands, and then a few other unrelated commands for good measure. In this second conference, Moses will be given a much longer and highly detailed set of instructions for the construction of the "Tent of Meeting", a.k.a. the tabernacle, the various holy objects associated with the tabernacle, and the establishment and provision for the priesthood. This is the definitive framework through which the Israelite people will interact with their new sovereign. I will add much more specific detail in later chapters, as we read through these new provisions, but I would like to urge my readers to view this as the LORD, for the first time, providing a definitive and concrete process whereby his new followers can seek his blessing in keeping with their new covenant. It is best to not view these as dead relics of a bygone era, but to view them in the light that the early Hebrews would have seen: the rituals through which they can "meet" their new God.