For if the blood of bulls and of goats, and the ashes of an heifer sprinkling the unclean, sanctifieth to the purifying of the flesh: How much more shall the blood of Christ, who through the eternal Spirit offered Himself without spot to God, purge your conscience from dead works to serve the living God? – Hebrews 9:13,14

Solomon, according to the Jewish tradition, declared that he did not understand why the ashes of the heifer made everybody clean except those who were unclean already. You saw in the reading that the priest, the man who killed the red cow, the person who swept up the ashes and he who mixed the ashes with water and sprinkled them were all rendered unclean by those acts—and yet the ashes purified the unclean! Is not this analogous to the riddle of the bronze serpent? It was by a serpent that the people were bitten—and it was by a serpent of brass that they were healed! Christ’s being regarded as unclean that we become clean and the operation of His Sacrifice is just like that of the ashes, for it both reveals uncleanness and removes it.

If you are clean and you think of Christ’s death, what a sense of sin it brings upon you! You judge of the sin by the Atonement. If you are unclean, drawing near to Christ takes that sin away!—

“Thus while His death my sin displays
In all its blackest hue,
Such is the mystery of Grace,
It seals my pardon, too.”

If we think we are unclean, a sight of the atoning blood makes us see how unclean we are. And if we judge ourselves unclean, then the application of the atoning Sacrifice gives our conscience rest. ~ C.H. Spurgeon

https://www.blueletterbible.org/comm/spurgeon_charles/sermons/1481.cfm