He shall purify himself with it on the third day, and on the seventh day he shall be clean: but if he purify not himself the third day, then the seventh day he shall not be clean. He shall purify himself with it - יתחטא בו yithchatta bo, literally, he shall sin himself with it. This Hebrew form of speech is common enough among us in other matters. Thus to fleece, to bark, and to skin, do not signify to add a fleece, another bark, or a skin, but to take one away; therefore, to sin himself, in the Hebrew idiom, is not to add sin, but to take it away, to purify. The verb חטא chata signifies to miss the mark, to sin, to purify from sin, and to make a sin-offering. See the note on Genesis 13:13.
The Hebrews generally sacrificed males, no matter of what color; but here a heifer, and a heifer of a red color, is ordered. The reason of these circumstances is not very well known.
"The rabbins, with all their boldness," says Calmet, "who stick at nothing when it is necessary to explain what they do not understand, declare that the cause of this law is entirely unknown; and that Solomon, with all his wisdom, could not find it out."
Several fathers, as well modern as ancient, profess to understand the whole clearly.
1. The red heifer with them signifies the flesh of our Lord, formed out of an earthly substance.
2. Being without spot, etc., the infinite holiness of Christ.
3. The sex of the animal, the infirmity of our flesh, with which he clothed himself.
4. The red color, his passion.
5. Being unyoked, his being righteous in all his conduct, and never under the yoke of sin.
6. Eleazar's sacrificing the heifer instead of Aaron, Genesis 13:3, signifies the change of the priesthood from the family of Aaron, in order that a new and more perfect priesthood might take place.
7. The red heifer being taken without the camp (Genesis 13:3) to be slain, points out the crucifixion of our Lord without the city.
8. The complete consuming of the heifer by fire, the complete offering of the whole body and soul of Christ as a sacrifice to God for the sin of man: for as the heifer was without blemish, the whole might be offered to God; and as Christ was immaculate, his whole body and soul were made a sacrifice for sin.
9. As the fire of this sacrifice ascended up to God, so it points out the resurrection and ascension of our blessed Lord.
10. And as the ashes of this victim communicated a legal purity to those who were defiled, so true repentance, signified by those ashes, is necessary for the expiation of the offenses committed after baptism.
A great part of this is true in itself; but how little evidence is there that all these things were intended in the ordinance of the red heifer? See on Numbers 8:7 (note).