Boil Your Pots and Self-Clean Your OvenBy Rabbi Jack Abramowitz
Everyone came out to greet the army, but Moshe was angry.
“Why did you allow the women to survive?” he asked them. “They were the ones involved in the plot against us!” He instructed that they execute the male children and the adult women who had been sexually active. Only the minor girls, not sexually active, were kept alive. (According to the Talmud in Yevamos 60b, G-d identified which women were guilty. The boys were presumably included so they wouldn’t grow up to do the “Hello. My name is Inigo Montoya. Prepare to die” thing.)
The soldiers had to remain outside of the camp for a week because of corpse contamination. They, their captives (who obtained the status of slaves) and their utensils had to undergo the purification process.
Elazar told the soldiers how to purify the vessels they acquired for use. Those things used in fire had to be purged with fire. Those used to heat water had to be boiled with water. Those items not used with fire at all merely needed to be immersed in a mikvah. (This is how we still render vessels kosher today.)