In their book Every Tribe and Tongue, Michael Pasquale and Nathan L.K. Bierma point out that the verb wash in Psalm 51 refers specifically to washing clothes. “The word actually means ‘to tread, to trample underfoot,’ since that’s how clothes were washed in ancient Israel. You’d put a dirty garment underwater and trample it to try to get it clean. The psalmist doesn’t just ask for a cleansing or a rinsing, but is saying to God, ‘trample my sins out, just like I try to tread on my clothes to get the stains out, pounding and grinding them with my feet.’”
The cleansing procedures described in Numbers 19 carry these spiritual themes as well. There is an overwhelming desire to stand pure and holy in God’s sight. To make the special “water of cleansing” required burning a red heifer outside the camp, along with some cedar wood, hyssop, and scarlet wool, all (red, like blood) symbols of purification (vv. 6–9). The ashes were then kept outside the camp and used to make holy water as needed.
A specific ritual with this holy water is described for cleansing after touching a corpse. It included bathing and washing one’s clothes in a prescribed manner. The ritual was not just a rote action but part of worship because it honored God’s holiness. Other ceremonies, such as the one for cleansing from skin diseases, were similar (see Lev. 14:1–11).
The writer of Hebrews later compared this holy water to the blood of Christ (Heb. 9:13–14). The first could only cleanse externally, whereas Christ’s saving blood can actually “cleanse our consciences” and make us spotless of sin. We desire to stand pure and holy in God’s sight, but we cannot do it on our own. We need His help to be made truly clean!