The Torah, “Leviticus” (Tzav), 6:9: And Aaron and his sons shall eat whatever is left over from it. It shall be eaten as unleavened bread in a holy place; they shall eat it in the courtyard of the Tent of Meeting.
Aaron is the great priest (Cohen). Priest (Cohen), bread, processed flour, and incense symbolize the attribute of bestowal in a person. This means that everyone takes his best attributes and brings them to complete bestowal for the benefit of others.
But only Aaron and his sons can eat the unleavened bread, the Matzot, since they are on the level of Bina, the attribute of complete bestowal. All the rest, who are not on that level, cannot eat this food since they will eat it in order to receive, and this is considered spiritual death.
Thus, Aaron and his sons ascend by working on the meal-offering, and all the others fall.
From KabTV’s “Secrets of the Eternal Book” 12/10/13