Exodus 32:27

Thus saith the Lord God. — Moses felt that he was divinely commissioned to perform this act of severity. The lives of all who had committed the idolatry were justly forfeit. Trial was unnecessary where the offence was being openly committed before the eyes of all. Such dancing and such shouting could not possibly be Jehovah-worship. It was by its very character idolatrous.

Go in and out from gate to gate... — i.e., “pass through the whole camp from end to end, visit all parts of it, and wherever you see the rites continuing, smite with the sword — smite, and spare not.”

Slay every man his brother. — Comp. Exodus 32:26. The Levites who had rallied to the call of Moses might find their own brothers or their own sons among the idolaters. If they did, they were still to smite, though the offender was their near relative.