Before the sanctuary and its vessels were dedicated for service, they were anointed with holy oil. On this occasion the miracle came to pass that twelve lugs of oil sufficed not only to anoint the sanctuary and its vessels, and Aaron and his two sons throughout the seven days of their consecration, but with this same oil were anointed all the successors of Aaron in the office of high priest, and several kings until the days of Josiah.
An especial miracle occurred when Aaron was anointed and on his pointed beard two drops of holy oil hung pendant like two pearls. These drops did not even disappear when he trimmed his beard, but rose to the roots of the hair. Moses at first feared that the useless waste of these drops of holy oil on Aaron's beard might be considered sacrilege, but a Divine voice quieted him. A Divine voice quieted Aaron, also, who likewise feared the accident that had turned the holy oil to his personal use. 
The anointing of Aaron and his two sons was not the only ceremony that consecrated them as priests, for during a whole week did they have to live near the Tabernacle, secluded from the outer world. During this time Moses performed all priestly duties, even bringing sacrifices for Aaron and his sons, and sprinkling them with the blood of these sacrifices.  It was on the twenty-third day of Adar that God bade Moses consecrate Aaron and his sons as priests, saying to him: "Go, persuade Aaron to accept his priestly office, for he is a man whom shuns distinctions. But effect his appointment before all Israel, that he may be honored in this way, and at the same time warn the people that after the choice of Aaron none may assume priestly rights. Gather thou all the congregation together unto the door of the Tabernacle." At these last words Moses exclaimed: "O Lord of the world! How shall I be able to assemble before the door of the Tabernacle, a space that measures only two seah, sixty myriads of adult men and as many youths?" But God answered: "Dost thou marvel at this? Greater miracles than this have I accomplished. The heaven was originally as thin and as small as the retina of the eye, still I caused it to stretch over all the world from one end to the other. In the future world, too, when all men from Adam to the time of the Resurrection will be assembled in Zion, and the multitude will be so great that one shall call to the other, 'The place is too strait for me, give place to me that I may dwell,' on that day will I so extend the holy city that all will conveniently find room there." 
Moses did as he was bidden, and in presence of all the people took place the election of Aaron and his sons as priests, whereupon these retired for a week to the door of the Tabernacle. During this week, in preparing the burnt offering and the sin offering, Moses showed his brother Aaron and Aaron's sons how to perform the different priestly functions in the sanctuary. Moses made a sin offering because he feared that among the gifts out of which the sanctuary had been constructed, there might have been ill-gotten gains, and God loves justice and hates loot as an offering, Moses through a sin offering sought to obtain forgiveness for a possible wrong. During this week, however, the sanctuary was only temporarily used. Moses would set it up mornings and evenings, then fold it together again, and it was not until this week had passed that the sanctuary was committed to the general use. After that it was not folded together except when they moved from on encampment to another. 
These seven days of retirement were assigned to Aaron and his sons not only as a preparation for their regular service, they had another significance also. God, before bringing the flood upon the earth, observed the seven days preceding as a week of mourning, and in the same way He bade Aaron and his sons live in absolute retirement for a week, as is the duty of mourners, for a heavy loss awaited them - the death of Nadab and Abihu, which took place on the joyous day of their dedication.