Tzaraas and zivah guard the two covenants

במד' איום ונורא הוא כו'.

In the Midrash on "He is awesome and dreadful (ayom v'nora)…"

The Sefas Emes cites the Midrash that expounds the phrase "ayom v'nora" (Chavakuk 1:7).

דורש על האדם.

It expounds this concerning man.

The Midrash applies "awesome and dreadful" to the human being himself.

והרמז על ברית הלשון והמעור.

And the allusion is to the bris halashon (covenant of the tongue) and the bris hama'or (covenant of circumcision).

The two words "ayom" and "nora" hint at the two covenants a person guards — the covenant of speech and the covenant of milah.

איום הוא הלשון שזה בחי' מדבר ששולט על כל הברואים ובזוה"ק וישב השומר פיו ממאכלות אסורות אימתו מוטלת על הברואים ע"ש בפסוק אל' שלח מלאכו וסגר פום אריותא מטעם שדניאל שמר עצמו מפת בג המלך.

"Ayom" (awesome) is the tongue, which is the aspect of speech that rules over all creatures; and in the Zohar Hakadosh, Vayeishev, one who guards his mouth from forbidden foods — his awe is cast upon the creatures, as on the verse "My God sent His angel and shut the mouths of the lions," because Daniel guarded himself from the king's food.

The covenant of the tongue (which includes guarding the mouth in speech and in food) gives a person mastery over all creatures. The Zohar links this to Daniel: because he refused the king's forbidden food, an angel sealed the lions' mouths, and his awe fell upon them.

ונורא הוא ברית המעור כמ"ש בזוה"ק ויצא בפסוק מה נורא המקום הזה שהוא חתימת שמו של המלך.

"Nora" (dreadful) is the covenant of milah, as stated in the Zohar Hakadosh, Vayeitzei, on the verse "How awesome (nora) is this place," which is the sealing of the King's Name.

The covenant of milah corresponds to "nora"; the Zohar connects it to Yaakov's words "how awesome is this place," since milah is the imprint of Hashem's Name sealed into the body.

ובזה דוחה כל הרוחות ומזיקין כמו דאיתא במזוזה שמבריח המזיקין מן הבית.

And through this one repels all the harmful spirits and destroyers, just as it is taught regarding the mezuzah, which drives away the destroyers from the house.

The seal of milah, like the Name on the mezuzah that protects a home, wards off all destructive spiritual forces.

ולכן מול ב' אלו הכוחות שבאדם משפטו ושאתו יצא.

Therefore, corresponding to these two powers within man, "his judgment and his dignity (s'eiso) go forth."

The two halves of the verse "his judgment and his dignity go forth from him" correspond to these two covenants within a person.

וניתן צרעת לשמירת ברית הלשון.

And tzaraas was given to safeguard the covenant of the tongue.

The affliction of tzaraas, which comes for lashon hara, serves to protect the covenant of the tongue by deterring misuse of speech.

וזיבה לשמירת ברית המעור כמ"ש במ"א מזה:

And zivah (the impure flux) was given to safeguard the covenant of milah, as explained elsewhere.

The laws of zivah serve to guard the covenant of milah, the holiness of the body, just as tzaraas guards the tongue.

Summary: The Sefas Emes reads the Midrash's "awesome and dreadful" as referring to the two covenants within every person: "ayom" (awesome) is the bris halashon, the power of holy speech that grants mastery over all creatures — exemplified by Daniel, whose guarding of his mouth shut the lions' mouths; and "nora" (dreadful) is the bris milah, the imprint of Hashem's Name sealed into the body, which repels destructive forces like the mezuzah guards a home. Corresponding to these two powers, tzaraas was given to safeguard the covenant of the tongue and zivah to safeguard the covenant of milah.