Exod 32:27

“The sons of Levi, who rallied to Moses with drawn swords, attacked them. But the sons of Levi did not know whom they should kill, because those who had worshiped mixed with those who had not worshiped. But the One for whom distinctions are easy to make separated those who committed idolatry from those who had not, so that the innocent would be grateful that their innocence had not escaped the notice of the just one, and the guilty would be brought to justice because their crime had not escaped the judge.”

“Let them hear how Moses, when he saw that God was angry with His people, and commanded swords to be taken for executing vengeance, declared those to be on God's side who should smite the crimes of the offenders without delay, saying, If any man is the Lord's, let him join himself to me; put every man his sword upon his thigh; go in and out from gate to gate through the midst of the camp, and slay every man his brother and friend and neighbour. For to put sword upon thigh is to set earnestness in preaching before the pleasures of the flesh; so that, when any one is earnest to speak holy words, he must needs have a care to subdue illicit suggestions. But to go from gate to gate is to run to and fro with rebuke from vice to vice, even to every one by which death enters in unto the soul. And to pass through the midst of the camp is to live with such impartiality within the Church that one who reproves the sins of offenders turns aside to shew favour to none. Whence also it is rightly added, slay every man his brother and friend and neighbour. He in truth slays brother and friend and neighbour who, when he finds what is worthy of punishment, spares not even those whom he loves on the score of relationship from the sword of his rebuke. If, then, he is said to be God's who is stirred up by the zeal of divine love to smite vices, he surely denies himself to be God's who refuses to rebuke the life of the carnal to the utmost of his power.”