Numbers 19:10

And he that gathereth the ashes of the heifer shall wash his clothes, and be unclean until the even, for he also became Levitically defiled by the performance of this task; and it shall be unto the children of Israel and unto the stranger that sojourneth among them for a statute forever; the special rites connected with the water of purification as prepared with the ashes were to be observed as long as the Levitical priesthood and its ordinances would endure. The Lord at all times wants pure and holy people as His servants.