While Moses was on the mount, God told him to go down. Moses turned and went down with the two tablets of testimony, the Ten Commandments, in his hands. As he drew near to the camp and saw the condition of the people, his wrath waxed hot and he cast down the two tablets. Standing at the gate of the camp he said, "Who is on the Lord's side? let him come unto me" (v. 26). All the sons of Levi gathered around him. He said to them, "Put every man his sword by his side, and go in and out from gate to gate throughout the camp, and slay every man his brother, and every man his companion, and every man his neighbor" (v. 27). Regardless of whom they saw, they had to kill them all. Because the people had worshipped the idol, the golden calf, those who were faithful had to draw their sword and slay them, no matter what kind of relationship they had with them.
Many people think that this order was too cruel. Who can slay his own brother? Who has the heart to kill his own friends? Eleven of the twelve tribes did not move. They felt that the cost was too high. As a result, only the tribe of Levi drew their swords, went to and fro from gate to gate throughout the camp, and slew about three thousand men on that day. Those slain were the brothers, relatives, and friends of the Levites.
Let us consider this a little. After the incident of the golden calf, God immediately told Moses that from that time on the nation of Israel could no longer be a kingdom of priests. Although nothing was said explicitly to that effect, God had reassigned the priesthood to the tribe of Levi alone. The priesthood was originally for the whole nation of Israel. Now, the priesthood was limited to the house of Aaron of the tribe of Levi.
From that time on, there were always two groups of people in the nation of Israel. One group were God's people and the other were God's priests. God's original intention was for all His people to be His priests. God had no intention of separating His people from His priests. He wanted the whole nation to be a kingdom of priests. God's people and God's priests should have been one. Whoever were God's people should have been His priests. As long as a person was one of God's people, he should have been God's priest. To be His people meant to be His priests. All His people were to be His priests. However, many loved the world and succumbed to human affection and turned away from faithfulness to worship the idol. As a result, God's people and His priests became two separate groups. Henceforth, if a man did not love the Lord more than his father, mother, wife, children, brother, sister, and all, he became unfit to be a disciple of the Lord. Many could not meet this requirement or pay this price. From that day forward, the nation of Israel was divided into two groups—God's people and His priests.
From that day forward, the kingdom of priests became a tribe of priests. The scope of the priesthood was reduced from a kingdom of priests to a household of priests. The priesthood became the matter of a household instead of a nation. God's people and God's priests were one and the same in the tribe of Levi; that is, His people were His priests. In regards to the other eleven tribes, God's people were only God's people; they could no longer be God's priests. This was most serious. It is serious for a person to be a believer, one of God's people, and yet not be a priest.