Charles Ellicott Commentary Numbers 19:4

"and Eleazar the priest shall take of her blood with his finger, and sprinkle her blood toward the front of the tent of meeting seven times." — Numbers 19:4 (ASV)

And Eleazar the priest shall take of her blood ... — The appointed rites were to be discharged by Eleazar, not by Aaron, who would otherwise have been temporarily disqualified by legal impurity from the discharge of his high-priestly functions.

Before the tabernacle of the congregation ... — that is, opposite to the entrance of the Tabernacle, but, as stated in the preceding verse, outside the camp, because the act had reference to the uncleanness of death.