Exodus 19

1 God did not lead the Israelites directly to the Promised Land. Since the Israelites had grown up in a pagan society God needed to reshape their hearts and minds. Up to this point, the Israelites had shown that they neither fully trusted God nor understood what He expected of them. God would prepare them by allowing them to hear His voice audibly and writing down His requirements. Although they were to receive the Ten Commandments and laws regarding proper worship, the Israelites would still have problems with their faith and obedience.
2 Moses led the Israelites to Mount Sinai, just as God had promised in Exo 3:12.
3 This completed the sign that God promised in Exo 3:12. Once Moses was at the mountain of Sinai with the Israelites, he could only acknowledge that God had done it.
5 God had given the Israelites adequate proof of His power, love, and trustworthiness. If they would now accept the evidence and love, trust, and obey God, He would continue to be with them.

God still works the same way today. God has said that He loves every person on the planet (John 3:16). He does not require us to love Him first. Instead He first proved His love towards us and asks that we love Him back (Rom 5:8). If we do, then we can look forward to the "Promised Land" of Heaven, where we will forever be in His presence. Those who do not trust God will be cut off from Him (and His gracious attributes) at death.

God has made the entire universe, so everything belongs to Him. It is His right to have a favorite people and to judge those who will not obey.

6 Every member of Israel was to act as a priest. Yes, there would be a special group of people designated as "priests," but everyone in Israel was responsible for learning about God and being able to tell others about Him. Through Jesus, Christians have inherited this blessing and responsibility (Rev 1:6).
7 Moses spoke God's words to the elders, and it was their responsibility to disseminate them to the rest of the people.
8 The elders were representatives of their families and clans. If an elder agreed to something, the people he represented were bound by duty to agree with it. This is similar to the representative form or democracy except that dissent was less frequent (or less vocal) and decisions were more rigorously followed. Duty, respect, and honor are what made their promises and laws enforceable. People's desire to keep their word is typically bolstered when they know that they will ultimately be accountable to God for their actions.
9 God told Moses that the Israelites were going to hear His voice. This was intended to dispel any notion that Moses was setting himself up as a ruler and making up marching orders and laws on his own.

God would appear in a thick cloud to hide His glory from the people. The sin-infested flesh would perish if one would gaze upon God's theophany, the manifestation of God's presence.

10 It is right for us to prepare ourselves to meet God. But this does not mean that washing our cloths is just enough. The people were to "consecrate" themselves. This means that they were to make a special effort to abstain from evil thoughts and actions, but instead focus their hearts on God.
12 Here is where we see how sin separates us from God. Even though these were His chosen people and they would be cleansed and consecrated, they would not be able to approach the epiphany (physical manifestation) of God. Anything that has even the slightest hint of sin can not approach God's presence with out being completely destroyed. As it turns out, God's manifestation was so frightening to the people that they did not even consider approaching the mountain (Exo 20:18).

Why was Moses able to approach God unharmed? It is possible that Moses was able to approach God because he already knew about Jesus, the Messiah (Deu 18:15, Mat 17:3, Heb 4:15, 16). Jesus' payment for sin was good, not just from His resurrection forward, but for the time that had already passed, too (Heb 10:12).

13 If God did not kill the offending person, then those who witnessed the violation were obligated to execute judgement. The executors were to stone or shoot the offender so that they would not touch him.
15 Part of consecration is to abstain from sex. The people were to focus on God for three days and not be distracted by their fleshly desires. Such abstinence between man and wife is never intended to be permanent (1 Cor 7:5).
16 God makes is presence known in many different ways. To Moses God first appeared in a burning bush. To the Israelites God showed His power first and then manifested Himself as a pillar of cloud and fire. Up to this point, the Israelites seem only moderately impressed. Now God makes a prominent and frightening appearance.
19 Trumpets were often used to announce the arrival of someone important.

As God had promised, He spoke to Moses in an audible voice so that all the people could hear Him.

21 The people had already been warned, but Moses was to warn them again. Moses would be on the mountain a long time with God, and the temptation to go and search for him would become strong. There would also be those who wanted to see if they could get a glance at God's glory without Him knowing about it. Such an irreverent act would result in death.
22 Those who had the special duty of serving God were to take purity seriously. To worship God in an unworthy manner was punishable by death.
23 The common people of that time were to stay further away from God. How fortunate we are as Christians to be able to approach God more closely (Heb 12:18-24).
24 The previous verse appears to be a protest on Moses' part. He has been up and down the mountain several times. The mountain was difficult to climb and Moses was getting weary of it. God, however, will not tolerate Moses' unwarranted frustration. He sends Moses away with a strong command and tells him to return with his brother. Aaron would become the first high priest, so it was important that he have a close encounter with God.
25 Moses knew better than to trifle with God. He had a momentary lapse, but quickly did what God asked after he was rebuked.