“Only the gold, the silver, the bronze, the iron, the tin, and the lead. Everything that can stand the fire, you shall pass through the fire, and it shall be clean” (v22-23). The Israelites had fallen into terrible idolatry with the Midianites/Moabites, so more than being Israel’s rivals, they were also a source of corruption (v16). Everything of theirs won in battle had to be symbolically cleansed, because it was all polluted.
“It shall be clean” (v23). Jesus passed through death for us, and His cleansing is not symbolic, but real. No matter our sin, then we claim His righteousness by faith, we become holy.