Korach: Chapter 6
"Do not cut off the tribe of the families of the Kohathites"

Rabbi Elazar says that the Levites can approach the Holy only through the priest, and that the priest hides and covers anything that they are not permitted to see. This is because everything of the priest is done in a whisper, secretly, while the Levites' speech and activities are in the raising of song and revelation of secrets. The priest's words are not spoken openly because he is of the right, Chesed. Rabbi Elazar tells us that when judgment prevails on the world from the left aspect, the right draws near by the burning of incense that is done quietly in secret. When Aaron ran into the midst of the congregation to stop the plague that was killing them he stood between the dead and the living, that is, between the Tree of Life and the Tree of Death. Thus the Tree of Life that is from the right came close to the priest, who was from the right, and the plague was stopped. Rabbi Elazar says that the priest has power above and below, and he is the cause of peace above and below; at all times the left serves the right.