17 "For the unclean person, put some ashes from the burned purification offering into a jar and pour fresh water over them. 18 Then a man who is ceremonially clean is to take some hyssop, dip it in the water and sprinkle the tent and all the furnishings and the people who were there. He must also sprinkle anyone who has touched a human bone or a grave or anyone who has been killed or anyone who has died a natural death. 19 The man who is clean is to sprinkle those who are unclean on the third and seventh days, and on the seventh day he is to purify them. Those who are being cleansed must wash their clothes and bathe with water, and that evening they will be clean. 20 But if those who are unclean do not purify themselves, they must be cut off from the community, because they have defiled the sanctuary of the Lord. The water of cleansing has not been sprinkled on them, and they are unclean.

Matthew Henry's Commentary on Numbers 19:17-20

Commentary on Numbers 19:11-22

(Read Numbers 19:11-22)

Why did the law make a corpse a defiling thing? Because death is the wages of sin, which entered into the world by it, and reigns by the power of it. The law could not conquer death, nor abolish it, as the gospel does, by bringing life and immortality to light, and so introducing a better hope. As the ashes of the heifer signified the merit of Christ, so the running water signified the power and grace of the blessed Spirit, who is compared to rivers of living water; and it is by his work that the righteousness of Christ is applied to us for our cleansing. Those who promise themselves benefit by the righteousness of Christ, while they submit not to the grace and influence of the Holy Spirit, do but deceive themselves; we cannot be purified by the ashes, otherwise than in the running water. What use could there be in these appointments, if they do not refer to the doctrines concerning the sacrifice of Christ? But comparing them with the New Testament, the knowledge to be got from them is evident. The true state of fallen man is shown in these institutions. Here we learn the defiling nature of sin, and are warned to avoid evil communications.