"Moses saw that the people were running wild and that Aaron had let them get out of control and so become a laughingstock to their enemies. So he stood at the entrance to the camp and said, 'Whoever is for the Lord, come to me.' And all the Levites rallied to him." (Exodus 32:25-26) The people have made fools of themselves. Everyone in the region will hear about how quickly they turned their backs on the God who brought them out of Egypt with mighty signs and wonders. This is something you and I, as Christians, need to take to heart. The world is watching us to see whether we are the real deal or not. I don't think anyone expects us to be perfect but they do expect to be able to get a glimpse of what Christ is like by observing how Christians live. If unbelievers don't find anything admirable in Christians then they're not likely to find anything admirable about Christ. They'll conclude that we're frauds and hypocrites and they'll conclude that Christ either doesn't exist or that He lacks the power to transform people's character. This is why Moses says that right now, in Exodus 32, his people are a laughingstock to their enemies. They look like a bunch of hypocrites. They quickly and easily abandoned God and are behaving like some of the worst of the heathen tribes in the region.
Moses wants to know who is still on the Lord's side and the tribe of Levi---his own tribe---comes and stands with him. We don't know if this means these men didn't partake in the idolatrous practices along with the others or whether these men were just the first to come to their senses. I think there's little doubt that there were degrees of sin in the camp. Some of the people probably sunk as low as they could go and gave in to every sinful desire of their hearts. Some may have only partaken in the feast of food that was presented to the idol but then did nothing further. Some sang and danced drunkenly but didn't engage in the adultery that the Apostle Paul says took place during the festival. (1 Corinthians 10:8) There very well may have been some members of the camp who distanced themselves from this sinful revelry and remained in their tents. We don't know everything that happened and we don't know who did what, but the Lord knew who the worst offenders were. It appears that these primary offenders are stubbornly unrepentant for everything they've done (and would do it all over again at the first opportunity) and this is why we find them facing a harsh judgment as we move on through our passage.
Now that the Levite men have made clear their allegiance to the Lord and to Moses, Moses gives them their orders. "Then he said to them, 'This is what the Lord, the God of Israel, says: 'Each man strap a sword to his side. Go back and forth through the camp from one end to the other, each killing his brother and friend and neighbor.' The Levites did as Moses commanded, and that day about three thousand of the people died." (Exodus 32:27-28) To our modern minds these two verses come across as puzzling, shocking, and maybe even offensive. These men strike down three thousand of their relatives, neighbors and friends. In asking why the Lord commands such a thing we need to consider how such a thing was carried out. Why did no one resist? Why did no one step up to defend any of the three thousand? Why did no one flee the camp and run off into the desert or up into the hills for safety? I think the best conclusion we can come up with is that somehow the Lord pointed these particular people out to the Levites, or else the Levites were aware of who the worst sinners in the camp were since the Levites had been present while the idolatrous feast took place. Perhaps they had observed who the ring leaders were of this whole mess. I think everyone in the camp probably knew which of the people had mobbed Aaron and demanded an idol. I think everyone knew which of the people made sacrifices to the idol, and which of the people engaged in a pagan orgy, and which of the people repudiated the one true God and said of the golden calf, "This is my god!" And it could be that, while the Levites move through the crowd, everyone stands back from those who are the worst offenders to allow the Levites to strike them down. They may even have hemmed the three thousand in so the Levites could carry out these orders.
Everyone in the camp bears some form of guilt, even if it's just the guilt of not speaking out against sin and idolatry, but it would seem that three thousand of them committed such horrible sins and are so unrepentant for those sins that it's best for the entire group if these three thousand are removed from their number. If they are allowed to remain they will continue to be a serious problem and will entice or force others into sin with them. The only thing we can really be sure of in this passage is that the Lord knows what He's doing. He knows the heart of every human being. He knows everything everyone has ever done or ever will do and I think He looked down through the years and saw that these three thousand were only going to grow worse and worse, dragging others down with them. If He'd allowed them to remain they would have taught their children wrong and their children would have grown up serving false gods and might never have turned to the living God. I believe souls were saved later on that might never have been saved if the Lord had allowed these three thousand to remain on the earth.
Moses commends the Levites for their obedience to the Lord in this matter. "Then Moses said, 'You have been set apart to the Lord today, for you were against your own sons and brothers, and He has blessed you this day.'" (Exodus 32:29) I'm reminded of several verses in the Bible where we're told that God is "no respecter of persons", meaning He judges impartially. If two sinners stood before Him who had committed the same acts, He wouldn't accept a bribe from the rich man and give him a free pass while imposing a penalty on the poor man. Likewise, He wouldn't pardon the poor man out of pity but punish the rich man. Difficult as our passage today may be for us to understand, the Levites were doing something the Lord Himself does: judging impartially. The Levites struck down whoever they were commanded to strike down regardless of who the person was or what status the person held in the community or even whether the person was related to them. Sin is sin, no matter who is doing the sinning, and in this case these particular sins were so heinous that God decided it was better for the nation as a whole if these three thousand were taken from their midst. The Levites obey Him and treat everyone in this group of three thousand the same. I am sure it was extremely difficult for them to do this, so Moses assures them that the Lord recognizes how hard it was for them and that the Lord will bless them for their obedience.
The discipline for sin is not finished. God will keep His promise to Moses not to wipe the Israelites out, but there is further judgment to come for the things that took place while Moses was on the mountain receiving instructions from God. Tomorrow we'll find a plague falling on the camp.