Rashi explains that, when Moshe Rabbeinu summoned Aharon, he also asked the zekeinim, elders, to join them. It was important for the zekeinim to hear/see that Al pi haDibur Aharon nichnas u’meshameish b’Kehunah Gedolah, v’lo yomru meieilav nichnas, “In accordance with the statement (dibur) of G-d, Aharon enters and officiates in the office of Kehunah Gedolah, and they should not say he enters the office of Kehunah Gedolah on his own.” Apparently, Moshe Rabbeinu was concerned that the people would criticize the appointment of Aharon HaKohen as Kohen Gadol. Thus, he underscored that it was al pi haDibur, by Hashem’s command. If Moshe wanted to impress the people, he should have inducted Aharon in front of them. The zekeinim were all scholars of note whose access to the spiritual sphere overshadowed anything achieved by the hamon am, ordinary Jew. Why call them, rather than the people?
Horav Yosef Nechemiah Kornitzer, zl, explains this practically. Concerning Moshe, Hashem said, “Behold! I come to you in the thickness of the cloud, so that the people will hear as I speak to you, and they will also believe in you forever” (Shemos 19:9).” Hashem told Moshe that He would speak to him from the midst of a thick cloud, but the entire nation would be able to hear the Divine Voice. Thus, they would all know that Hashem had spoken to Moshe. Rav Kornitzer explains that, while Moshe was the pillar of Torah and elevated far above the nation, he was nonetheless a kvad peh u’kvad lashon, a stammerer. Physical challenge is no barrier with regard to spiritual distinction. Moshe’s speech impediment did not obstruct his ability to become the quintessential Rebbe and leader of Klal Yisrael. The people, however, were unable to perceive his greatness. It was only Aharon and the zekeinim who were acutely aware of Moshe’s eminence. Therefore, it was vital that Hashem speak to Moshe from within the thick cloud, so the people would believe and accept that Moshe was their appointed leader, chosen by the Divine Himself.
Let us turn the coin and focus on Aharon. The man destined to become Kohen Gadol was known for his love and pursuit of peace. His ability to convince and reach out to people of all backgrounds was legendary. He saved countless marriages and helped heal the rifts that often arise between people who had once been good friends. Aharon was a man of the people: loved, respected and admired by the hamon am, who were greatly indebted to him. The zekeinim, however, did not interact with him, because he did not need to inspire them to learn in order to maintain good relationships among themselves. These were individuals who were the spiritual elite, who were far beyond the petty differences that plague the ordinary Jew. When Hashem appointed Aharon to the Kehunah Gedolah, the people were not surprised. They revered him and knew he was capable of spiritual leadership. The zekeinim, however, were unaware of Aharon’s greatness. They did not know him. Thus, Moshe called them together and said, Al pi hadibur hu nichnas, “He is ascending to this lofty position because of the power of his dibur.” His ability to speak to everyone, to convince opposing sides to sit down at the table to iron out their differences, distinguished Aharon. The Kohen Gadol represents the nation in bringing the people closer to Hashem. As such, he must be a person people respected, admired and loved. His talent for saying the right thing at the right time, to assuage people’s feelings and calm them down, earned him the highest spiritual accolade. His dibur was his defining characteristic.
