Three months have passed since Israel left Egypt. Since they left bondage. Now, the sign that God promised to Moses is coming to fruition (Exod. 3:12). On this mountain, they were to “serve” God. This is a cognate of “tend” (ovda) in Genesis 2:15, which denotes priestly service (cf. Num. 3:7–10). This is fitting because God tells Israel that He intends for them to be a kingdom of priests and a holy nation (Exod. 19:6). God’s royal decree to Adam and Eve was to “subdue [the earth]; have dominion” over every living thing (Gen. 1:28). God gave the first humans both a royal and priestly service. The fall interrupted their ability to carry it out. He has now passed that service to Israel. Priests mediate humans to the divine and the divine to humans. As a “holy nation,” if they keep God’s commands, they would mediate between God and the nations, a promise God had made to Abraham (Gen. 12:3). As far as a timeline of events goes, beginning in Exodus 19—through Leviticus—and ending in Numbers 10 is one year of Israel camping at Mt. Sinai.
Thus far, Moses and God have spoken with one another. Moses goes and informs the people of what God has said, and he returns to God to relay their affirmation of these very things. Then, God is preparing to appear in the presence of the Israelites, but before they do so, they are to prepare (Exod. 19:10–13). This would occur over three days. We have to imagine that they’ve been traveling for a few months and probably haven’t bathed or changed clothes. Perhaps they stunk and needed to do laundry. Still, the cleanness they were to appear as was appropriate for appearing before God. Boundaries are established around the mountain to show the demarcation between the sacred and the common. Wherever God is, there is holiness. Were sinful commoners to approach such holiness, the result would be catastrophic. When the third day came, Israel saw a frightful sight (Exod. 19:16–19). God once more orders Moses to remind Israel to respect the boundaries set.
The following few chapters demonstrate God’s ordering of society. Various commands, general and specific, are given—the most famous of which is the Ten Commandments. The first three have to do with respecting God, and the last seven have to do with one’s neighbor. Thus we see the first and greatest command reflected here and the second, which is like unto the first. After that, specificity reigns until chapter 24 and is referred to as the Book of the Covenant. Afterward, Moses, his brother and nephews, and seventy elders go up the mountain. Moses recounted all of God’s words, and the people assent to His law.
Early in the morning, Moses built an altar at the base of the mountain. He set up twelve columns for the twelve tribes of Israel. Offerings and sacrifices were made, the blood was taken and used to cleanse the altar and the people. Then, he and those bid to come up the mountain do so. They see God and eat and drink. Sacrifice was always followed by a communal meal of the worshippers. Notice the similarities of these events to Christianity: the Word of God is given, recorded, read, and assented to by God’s people. The sacrifice of Jesus, His body and blood, are what we partake of every Lord’s Day as a community of God’s people. We, too, eat and drink, and we do so in God’s presence. The continuity is astounding.
The preacher of Hebrews informs us of our New Covenant in light of this first covenant (Heb. 9:18–20). These sacrifices, however, were ineffective at the atonement of humanity to God (Heb. 10:1–4). Those can never take away sins like the blood of Christ (Heb. 10:11–14). God set up this system to prepare us for that which was to come. We eat from an altar far superior to the one given to Moses and Israel (Heb. 13:10). Under the Old Testament, priests were given portions of most sacrifices, but laypeople couldn’t partake. As Christians, we all partake.
 Enns, Exodus for Normal People, 22–23.