Num 19:17-20 Ceremony of purification. They were to take for the unclean person some of the dust of the burning of the cow, i.e., some of the ashes obtained by burning the cow, and put living, i.e., fresh water (see Lev 14:5), upon it in a vessel. A clean man was then to take a bunch of hyssop (see Exo 12:22), on account of its inherent purifying power, and dip it in the water, on the third and seventh day after the defilement had taken place, and to sprinkle the tent, with the vessels and persons in it, as well as every one who had touched a corpse, whether a person slain, or one who had died a natural death, or a grave; after which the persons were to wash their clothes and bathe, that they might be clean in the evening. As the uncleanness in question is held up as the highest grade of uncleanness, by its duration being fixed at seven days, i.e., an entire week, so the appointment of a double purification with the sprinkling water shows the force of the uncleanness to be removed; whilst the selection of the third and seventh days was simply determined by the significance of the numbers themselves. In Num 19:20, the threat of punishment for the neglect of purification is repeated from Num 19:13, for the purpose of making it most emphatic.