26 So he stood at the entrance to the camp and shouted, "All of you who are on the Lord 's side, come here and join me." And all the Levites gathered around him. 27 Moses told them, "This is what the Lord, the God of Israel, says: Each of you, take your swords and go back and forth from one end of the camp to the other. Kill everyone-even your brothers, friends, and neighbors." 28 The Levites obeyed Moses' command, and about 3,000 people died that day. 29 Then Moses told the Levites, "Today you have ordained yourselves for the service of the Lord, for you obeyed him even though it meant killing your own sons and brothers. Today you have earned a blessing."
Matthew Henry's Commentary on Exodus 32:26-29
Commentary on Exodus 32:21-29
(Read Exodus 32:21-29)
Never did any wise man make a more frivolous and foolish excuse than that of Aaron. We must never be drawn into sin by any thing man can say or do to us; for men can but tempt us to sin, they cannot force us. The approach of Moses turned the dancing into trembling. They were exposed to shame by their sin. The course Moses took to roll away this reproach, was, not by concealing the sin, or putting any false colour upon it, but by punishing it. The Levites were to slay the ringleaders in this wickedness; yet none were executed but those who openly stood forth. Those are marked for ruin who persist in sin: those who in the morning were shouting and dancing, before night were dying. Such sudden changes do the judgments of the Lord sometimes make with sinners that are secure and jovial in their sin.