Matthew Poole and continuators on Exodus 32:27

27 And he said unto them, Thus saith the LORD God of Israel, 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 neighbour.

The meaning, Slay every principal offender, whom you meet with without any indulgence or exception for brother or companion or neighbour. There was no fear of killing the innocent in this case, because, 1. the people were generally guilty. 2. Moses had called to himself all that were on Gods side, who thereby were separated from the guilty: 3. the nocent might easily be discerned from the transgressours, either by the personal knowledge which the Levites or others had of the most forward Idolaters, or by their abiding in their tents as ashamed and grieving for their sin whilest the transgressours were impudently walking about in the camp, as trusting to their numbers, or by the direction of Gods providence, if not by some visible token.