Leviticus 8:4

4.And Moses did as the Lord commanded him Although these things relate to the priesthood, the authority and nature of which I expounded under the Second Commandment, yet, inasmuch as they are historical, it is not without reason that I have thought fit to defer them till this place: for, if I had referred to them in connection with the Commandment, unpractised readers would not have easily taken notice of their time. This distinction, however, will be of great assistance to them, that after the doctrine which was properly contained in the Decalogue has been set forth, they will now see how faithfully Moses fulfilled whatever he was commanded, and will be able to compare his obedience with the injunction, as they have done in the whole of the making and dedication of the tabernacle. Besides, there is no question but that the narrative must be thus connected; for it may be readily inferred from many passages, that the priests were anointed on the same day that the tabernacle was consecrated. I will now hastily run through the words. Moses says that he brought near Aaron and his sons, i.e., to set them before God and the people; and then that he “washed them with water,” to make it manifest that they did not bring from their homes the purity which befitted the sanctity of their office, and, inasmuch as they were men, that they could not be clean before God, unless their impurity was washed off. A description of their apparel afterwards follows, which I pass over, lest I should weary my readers by twice repeating the same thing.