The cohen, or priest, is a special subclass within the Jewish people. The priestly class was descended directly from Aharon. And the duties of a priest are spelled out in great detail in the Torah.
Why? What does it take to be a priest?
To understand this, we must start (as always) with the words of the Torah itself. Basically, the tasks of a priest are to keep the divine home (including tasks such as lighting the menorah, and handling the showbreads), and act as an interlocutor between mankind and Hashem, primarily through the sacrifices.
But in order to be able to perform these tasks, the priest has to do some very specific things. For starters, he has to wear a uniform. And that uniform serves a purpose, as I have argued before, of helping the wearer to understand that, when serving, there is no room for individuality. A priest has to be cognizant of the fact that he is supposed to be no more, and no less, than any other cohen before or after who has worn the same garments. There is no room for flair or style when serving in G-d’s House – a cohen can not add “a little something” to an incense offering, or improvise by altering how a sacrifice is made. Displaying individuality, leads, as in the case of Aharon’s sons, to an instant death. The cohen wears a uniform to remind themselves at all times that they are working within an extremely defined role.
What is the problem with individuality? We know that, in order for Hashem to exist in the Beis Hamikdash, that he has to limit Himself – that it is a compromise even for Hashem to “be” in any given space. After all, G-d is infinite. Space, on the other hand, is definable: it is ultimately finite.
So for G-d to exist in the Beis Hamikdash, He limits Himself.
And the Torah tells us that cohanim also have to limit themselves. Specifically, a cohen has to limit a key attribute of humanity: he has to limit his creativity.
And so while outside the Temple, we would praise a chef who experiments with a recipe, with words like “flair”, or “creativity,” there is no room for creativity in G-d’s house. Even more than this! The Cohen could not even be seen to be endowed with creative powers. And that is why the Torah tells us that a cohen has to wear a garment to specifically cover his private parts even from the view of the ground. Loins have creative power – which we are commanded to use – but not in G-d’s house!
And even more remarkably, in a religion which is all about words – from the Torah itself to the nature of prayer – a religion that uses words to create festivals and Shabbos and all manner of blessings: the Torah itself never commands the cohen to speak. Speech is the recycling of G-d’s breath. It is the use of the divine spirit that Hashem breathed into Adam – creativity incarnate! And the cohen serves in complete silence! He is not allowed to create anything new in the Beis Hamikdash!
Put all this together, and we see that cohanim have to be careful to limit themselves in order to coexist with the divine presence. They have to be exceptionally accommodating, willing to do whatever was necessary to themselves in order to please Hashem and keep the Beis Hamikdash peaceful.
And now we know why Aharon was the first high priest. Aharon, unlike Moshe, was phenomenal at seeking peace, and avoiding conflict. He did everything to avoid an argument. When tasked to speak for Moshe, Aharon accepts his role. Throughout his life, Aharon does what is expected of him. When the people demand the making of the egel, the golden calf, Aharon even accommodates those effectively heretical demands! Lastly, when Aharon’s sons are killed after bringing “strange fire” as an offering, Aharon performs the divine service without saying a single word.
Aharon’s traits are not universally praised or even desired! Moshe has a completely different character, arguing with G-d and man alike. But Jews come in all flavors, and what is most important is to have a job that matches the man. Aharon’s accommodating nature is dangerous when he is left to “lead” the people, as we know from the story of the golden calf. But that same desire to get along with others is an absolutely perfect fit to serve in G-d’s house, in a place where the demands on the self-denial of the priest are absolute.
And this is why it is Aharon who is the archetype for all high priests throughout the ages, and why every cohen has to be descended from the first. It takes a true rodef shalom, pursuer of peace, to be able to limit his very creativity in every respect, to serve G-d in silence at all times, even when he has just lost his sons. This is the greatness of Aharon – and why those of us who are not cohanim can and should appreciate that we are meant to serve G-d in other ways.