God's Covenant with Israel
God reiterated His covenant with Israel to His servant Moses. Moses called for the elders of Israel and repeated God's words to them. The elders then repeated the words to the people of Israel. This gives a clearer explanation of how Moses communicated with nearly three million people. Now we come to the point where God was planning to speak with Moses and all the people would be able to hear God's voice. But there were special instructions for the people to follow before they could approach the vicinity of God's holy presence. Boundaries were set about the mountain so the people would be restricted from touching it. The prohibition against touching the mountain was to teach them a sense of awe and respect toward the living God—and to demonstrate their need for a mediator. The people were to be clean, having their clothes washed. And on the day that God appeared to Moses on the mountain, married couples were to forego sexual relations. Wearing clean clothes and abstaining from marital relations were outward acts signifying that they had sanctified themselves before God spoke to them. This does not imply that lawful sexual relations are spiritually unclean. In the New Testament, Paul suggested that it is occasionally appropriate to refrain from marital relations for a brief time,when specially devoting that time to God through prayer and fasting (1 Corinthians 7:5). After Moses ascended the mountain, God had to send him back down because curiosity was getting the better of the people. After once again warning the people, Moses again ascended the mountain with Aaron.
The timing of all of this is very interesting. Jewish tradition asserts that the giving of the law occurred on the Feast of Firstfruits or Pentecost, which can occur no later than the 10th or 11th day of the third month of the Hebrew calendar, Sivan. Verse 1 does say that it was in the third month after leaving Egypt—but some interpret the phrase "on the same day" here to mean the same day of the month that the Israelites left Egypt. This, however, would mean that they arrived at Mount Sinai on the 15th of Sivan, with the law being given on the 17th (compare verses 10-11)—too late for Pentecost. However, if the phrase "on the same day" is understood to mean the same day that Jethro departed, as stated in the previous verse (18:27), then Pentecost can fit quite well. It could also be that the "same day" meant the same day of the week the Israelites had left Egypt—which, again, would allow for the Ten Commandments to have been delivered on Pentecost.
Indeed, there are clear Pentecost themes to be found here: the consecration of Israel as the chosen people, i.e. "firstfruits"; the beginning of the Old Testament "church in the wilderness" (Acts 7:38 KJV), as Pentecost would mark the beginning of the New Testament Church (see Acts 2); the giving of the law, as God's people would later be given the power to keep that law through the Holy Spirit on Pentecost (compare Luke 24:49; Romans 8:7); God descending on the mountain with great noise and trembling and "in fire" (Exodus 19:18), as His presence would later descend upon Christ's disciples with great noise and in tongues of fire (Acts 2); the initiation of the Old Covenant, as Pentecost would later mark the giving of the "better promises" of the New Covenant, particularly the gift of the Holy Spirit (compare Hebrews 8:6). Though typical of the new relationship God wants with His people, the Old Covenant still involved separation from God, as the boundary markers so vividly picture. To see this even more, read Hebrews 12:18-28.
The contrast between the Old and New Covenants is vividly illustrated by comparing two scriptures. "You shall set bounds for the people all around" (Exodus 19:12) and "let us draw near with a true heart in full assurance of faith" (Hebrews 10:22). Through Jesus Christ's sacrifice and intercession as our High Priest today, God has granted us liberty to come right before His very throne of grace (Hebrews 4:14-16).
Supplementary Reading: "The Feast of Pentecost: The Firstfruits of God's Harvest", God's Holy Day Plan: The Promise of Hope for All Mankind, pp. 24-29.