31:19-24 The Israelites had to purify themselves according to the law, and to abide without the camp seven days, though they had not contracted any moral guilt, the war being just and lawful, and commanded by God. Thus God would preserve in their minds a dread and detestation of shedding blood. The spoil had been used by Midianites, and being now come into the possession of Israelites, it was fit that it should be purified.And ye shall wash your clothes on the seventh day,.... As the leper did, Leviticus 14:9,

and ye shall be clean, and afterward ye shall come into the camp; into the camp of Israel, into the camp of the Levites, and into the camp of God, the tabernacle.