Parshas Shemini begins with the Posuk: “And it was on the eighth day, that Moshe summoned Aharon and his sons and the elders of Israel.” 9:1. In the previous Parsha Tzav we learned about how Hashem declared Seven Days of Miluim. During these seven ceremonial days of the inauguration of the Mishkan, Moshe Rabbeinu acted as the Kohen Gadol. This was the only time in his life that Moshe acted as Kohen Gadol. Now it is the eighth day, following this seven day period. Moshe called to Aharon and his four sons to invest them, and their descendants with the status of Kehuna for the rest of eternity.
Rashi asks: Why did Moshe have to summon the elders of Israel? And answers: To inform them that it was by the express command of Hashem that Aharon was entering into the Kehunah Gedolah, so that they should not say that he entered of his own accord. Therefore, Hashem told the elders that the idea came from Hashem and not from Aharon. The Gaon Harav Reb Dovid Pardoh, in his sefer Maskil Ledovid asks a difficult question: We see at the end of the previous Parsha 8:30, And Moshe took some of the anointing oil and some of the blood that was on the altar, and he sprinkled it on Aharon and on his garments, and on his sons, and on his sons' garments, and he sanctified Aharon, his garments, his sons and his sons' garments with him. In this case we see clearly that Moshe anointed Aharon which was commanded by Hashem. Therefore, how would the elders and others have a doubt that Aharon was entering the Kehuna on his own accord? Another Posuk states clearly that And Aharon and his sons did all the things that Hashem commanded through Moshe.
Rashi explains: And Aharon and his sons did all the things. To tell their praise, namely, that they did not deviate to the right or to the left. Here we see that the whole scenario of the seven days of preparations done through Moshe, and the anointing oil and blood which was placed on Aharon and his sons, was the command of Hashem. There are many commentaries which try to explain, why did Hashem give over the seven days to Moshe to act as a Kohen?
The Alschich Hakadosh writes that during the Seven Days of Miluim, even though Moshe Rabbeinu was acting as a Kohen, the Shechina, Divine Presence did not rest upon the Mishkan, and that fire did not descend from Heaven until the eighth day. The miraculous descent of fire from Heaven and the appearance of the Shechina in the Mishkan only took place the eighth day, when Aharon became Kohen. Until then, in effect, the Mishkan was an Empty House, bereft of G-d’s Presence. The Alshich explains that Hashem was doing to Moshe Rabbeinu, measure for measure for Moshe’s hesitancy to accept his mission to lead the Jews out of Egypt. For seven days, when Hashem asked Moshe to take the Jews out of Mitzrayim, He told Moshe, “Don’t worry! I will be with you.” Shemos 3:12 Moshe refused. There was an ongoing conversation that lasted for seven days, until Moshe Rabbeinu finally accepted the job on the eighth day. Moshe hesitated from his humility and his fear of offending his older brother. But, nevertheless, he said “No” to the Almighty for seven days. The Ba’al HaTurim explains because Moshe Rabbeinu refused to listen (initially) to the Ribono shel Olam, and stalled for seven days by the Burning Bush before accepting his mission, he was now rewarded by being given the opportunity to serve as Kohen Gadol—but only for seven days.
However, it came to me c''qa that we can say a powerful insight to understand what has transposed through the seven days of Miluim and of giving the Kehuna to Aharon: Moshe was at a higher level than Aharon and was destined to be Kohen. Hashem took it away from Moshe and gave it to Aharon. But, now it came the time to place the Kehuna for eternity and have the Shechina rest on the Mishkan. In order to set the stage, it had to have a very holy preparation. Hashem wanted only Moshe to make the preparations to such a holy event, because he was the superior person for this. We see Chazal that Aharon saw the Avodah from Moshe, and he was very happy at what he saw. This was the reason for his happiness, realizing how important the work of Moshe was. It says from Talmidei Baal Shem Tov that the preparation of a Mitzvah is as strong or even greater then the Mitzvah itself. Hence, Moshe was the real Kohen and his spiritual level stayed on in the Mishkan. Moshe had to come forth to the elders and calm them, that everything that transposed in the preparations, was from Hashem, in order to have the Shechina rest in the Mishkan and to prepare an eternal Kehuna for Aharon and his children.
(Yehuda Z. Klitnick)