Hebrews 9:13

For if the blood of bulls and goats, and the ashes of an heifer sprinkling the unclean, sanctifieth to the purification of the flesh;

2 Corinthians 5:21

For He hath made Him, who knew no sin, to be a sin-offering for us, that in Him we might be made righteous before God.

2 Corinthians 7:1

Having therefore, my beloved, these promises, let us purify ourselves from all defilement of flesh and spirit, perfecting holiness in the fear of God.

Hebrews 7:26

For such an high-priest was meet for us, who was holy, harmless, undefiled, separate from sinners, and higher than the heavens;

Treasury of Scripture Knowledge

Summary

And a man that is clean shall gather up the ashes of the heifer, and lay them up without the camp in a clean place, and it shall be kept for the congregation of the children of Israel for a water of separation: it is a purification for sin.

A water of separation

Bible References

Clean

2 Corinthians 5:21
For He hath made Him, who knew no sin, to be a sin-offering for us, that in Him we might be made righteous before God.
Hebrews 7:26
For such an high-priest was meet for us, who was holy, harmless, undefiled, separate from sinners, and higher than the heavens;
Hebrews 9:13
For if the blood of bulls and goats, and the ashes of an heifer sprinkling the unclean, sanctifieth to the purification of the flesh;

A water of separation

2 Corinthians 7:1
Having therefore, my beloved, these promises, let us purify ourselves from all defilement of flesh and spirit, perfecting holiness in the fear of God.