Numbers 18:7

Therefore thou and thy sons with thee shall keep your priest's office for everything of the altar, all the service connected with the golden altar of incense, where the priests were daily employed, and within the veil, for the high priest entered into the Most Holy Place once every year, on the great Day of Atonement, Leviticus 16:2; and ye shall serve. I have given your priest's office unto you as a service of gift, out of free grace and mercy, to stimulate all the greater diligence; and the stranger that cometh nigh shall be put to death, since this service was the exclusive duty of the family of Aaron. In a far better and higher sense it is true that we Christians have been given the rights of the universal priesthood of the New Testament by God's free gift in Jesus Christ, whence it follows that we should appreciate this blessing all the more highly.