19 You yourselves will have to keep outside the tent-circle for seven days, anyone of you who has put any person to death or come near a dead body; and on the third day and on the seventh day make yourselves and your prisoners clean.
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.
Matthew Henry's Commentary on Numbers 31:19
Commentary on Numbers 31:19-24
(Read Numbers 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.