Bilangan 19:18

19:18 Then a ceremonially clean person must take hyssop, dip it in the water, and sprinkle it on the tent, on all its furnishings, and on the people who were there, or on the one who touched a bone, or one killed, or one who died, or a grave.

Bilangan 31:20

31:20 You must purify each garment and everything that is made of skin, everything made of goat’s hair, and everything made of wood.” ¹ 

[31:20]  ¹ sn These verses are a reminder that taking a life, even if justified through holy war, still separates one from the holiness of God. It is part of the violation of the fallen world, and only through the ritual of purification can one be once again made fit for the presence of the Lord.