Aharon draws the distant near in peace

וכתיב באהרן ברית מלח עולם.

And it is written regarding Aharon, "an eternal covenant of salt" (Bamidbar 18:19).

The Sefas Emes opens with the "covenant of salt" given to Aharon and his descendants, and will explain what salt represents.

דאיתא מים תחתונים בוכים אנן בעינן למיהוי קרוב למלכא.

For it is taught: the lower waters weep, [saying,] "We too wish to be near the King."

When the waters were separated at creation, the lower waters wept at being cast far from Hashem's presence, longing for nearness.

והקב"ה הבטיח להיות מלח וניסוך המים במקדש.

And the Holy One, blessed is He, promised that there would be salt and the water-libation (nisuch hamayim) in the Mikdash.

Hashem consoled the lower waters by promising them a place on the altar — as salt on every offering and as the water poured on Sukkos.

ומעין זה הי' בנפשות תחתונים שנתרחקו מעל שולחן אביהם ונתן לנו הקב"ה את אהרן שהוא כמלאך ה' צבאות גם למטה ועל ידו מתקרבים התחתונים לעליונים ובזה יש שלום בעולם.

And something of this same nature existed among the lower souls (nefashos), who were distanced from their Father's table; and the Holy One, blessed is He, gave us Aharon, who is "like an angel of Hashem of Hosts" even below, and through him the lower ones are drawn near to the upper ones — and in this there is peace (shalom) in the world.

Just as the lower waters were comforted, so the distant lower souls were given Aharon, who like the weeping waters' salt bridges below and above, drawing the lower souls near to the heavenly realm and thereby making peace.

והיא עדות על כל כלל ישראל שנקראו השולמית שהשלום נמצא ביניהם כמ"ש במ"א מזה:

And it is a testimony upon all of Klal Yisrael, who are called "the Shulamis," that peace (shalom) is found among them, as I have written elsewhere on this.

Aharon's covenant of peace testifies that all of Yisrael — called "Shulamis," from shalom — are a people in whom peace and unity dwell.

Summary: The "covenant of salt" given to Aharon mirrors Hashem's promise to the weeping lower waters that they would be brought near through the salt and water-libation of the Mikdash. So too the distant lower souls were given Aharon, who is like an angel even here below and who draws the lower realm near to the upper, establishing shalom in the world. This is the testimony of Aharon's covenant upon all Klal Yisrael, the "Shulamis," a people in whom peace dwells.