Then a man who is ceremonially clean is to gather up the ashes of the heifer and store them in a ceremonially clean place outside the camp. They must be kept by the congregation of Israel for preparing the water of purification; this is for purification from sin.
We have here the divine appointment concerning the solemn burning of a red heifer to ashes, and the preserving of the ashes, that of them might be made, not a beautifying, but a purifying, water, for that was the utmost the law reached to; it offered not to adorn as the gospel does, but to cleanse only.
Commenting on Numbers 19:1-10
And a man that is clean shall gather up the ashes of the heifer,.... A man, a clean priest, as the Targum of Jonathan; in later times great care was taken that the priest concerned in the burning of the red cow should be pure; he was separated from his own house seven days before the time, and every day he was sprinkled with the...
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.