Albert Barnes Commentary Numbers 19

The principle that death and everything related to it, as the manifestation and result of sin (Genesis 2:17), are defiling, and thus lead to interruption of the living relationship between God and His people, is not introduced now for the first time, nor is it at all unique to the Mosaic law.

On the contrary, it was traditional among the Israelites from the earliest times; it is assumed in various enactments already made (Numbers 9:6 and following; Leviticus 10:1, 7; Leviticus 11:8, 11, 24; Leviticus 21:1 and following), and it is traceable in various forms among many nations, both ancient and modern.

Moses, here as elsewhere, adopted existing and ancient customs, with significant additions, as aids in the spiritual education of his people.

The ordinance was probably given at this time because the plague that occurred (Numbers 16:46–50) concerning the matter of Korah had spread the defilement of death so widely through the camp that it seemed to require special measures of purification, especially since the deaths resulting from it were, in an extraordinary way, the penalty of sin.

A red heifer – Red, to foreshadow humanity's earthly body, just as the name Adam alludes to the red earth from which the human body was formed.

Without spot, wherein is no blemish – As with sin offerings generally (Leviticus 4:3).

Upon which never came yoke – So here and elsewhere (see the marginal references), in the case of female victims.

The work would necessarily require a priest; yet, as it made him unclean for the day (Numbers 19:22), the high priest was relieved from performing it.

Without the camp - The defilement was viewed as transferred to the victim that was to be offered for its removal. Under these circumstances, the victim, like the defiled persons themselves, would be removed outside the camp. The particular pollution to be remedied by this ordinance was the indirect one resulting from contact with tokens and manifestations of sin, not the direct and personal one arising from actual commission of sin.

Likewise, the sinless antitype had to bear the reproach of associating with sinners (Luke 5:30; Luke 15:2). And as the red heifer was expelled from the precincts of the camp, so was the Saviour significantly cut off during His Life from the fellowship of the chief representatives of the theocracy, and put to death outside Jerusalem between two thieves .

Compare Leviticus 14:4 note.

Water of separation - In Numbers 8:7, the water of purification from sin is the water of purifying. So that which was to remedy a state of legal separation is here called “water of separation.”