Aharon's pure fear is the root of purity

במד' יראת ה' טהורה עומדת כו' מורא שנתירא אהרן זכה לדורות כו' ובמד' ויקרא ממתים ידך ה' כו' ע"ש שדורש על אהרן.

In the Midrash: "The fear of Hashem is pure, enduring forever" (Tehillim 19:10) — the awe with which Aharon was filled merited [the priesthood] for generations. And in Midrash Vayikra: "From men [whose portion is in life], by Your hand, Hashem" (Tehillim 17:14) — see there, where it is expounded regarding Aharon.

The Sefas Emes opens with two Midrashim linking Aharon to the trait of pure yiras Hashem and to a "portion in life" granted by Hashem's own hand.

דהנה יראת ה' לחיים היא יראה הרוממות וכהן עובד ה' במקדש חל עליו מורא שמים כמלאך משרת.

For behold, "the fear of Hashem unto life" is yiras haromemus (the awe of His exaltedness); and a kohen who serves Hashem in the Mikdash has the awe of Heaven rest upon him like a ministering angel.

This pure fear is not dread of punishment but awe before Hashem's greatness — the very awe that descends upon a kohen serving in the Bais Hamikdash, making him like a malach.

דאיתא אין מדותיו של הקב"ה כב"ו מוראו על הקרובים יותר כדכ' וסביביו נשערה מאוד.

For it is stated: the ways of Hashem are not like those of flesh and blood — His awe rests more upon those who are close to Him, as it is written, "And around Him it storms mightily" (Tehillim 50:3).

Unlike a human king, before whom familiarity breeds ease, the closer one draws to Hashem the greater the awe — those nearest to Him are most overwhelmed by His presence.

ועיקר היראה ממלכות שמים הי' בבהמ"ק.

And the essential fear of the kingship of Heaven was in the Bais Hamikdash.

The Mikdash was the supreme place where awe of Hashem's malchus was felt.

וגם בנ"י קיבלו יראה זו ג"פ בשנה כדכתי' יראה כל זכורך.

And Bnei Yisrael too received this fear three times a year, as it is written, "[Three times a year] all your males shall appear (yei'ra'eh) [before Hashem]" (Shemos 23:17).

Through the shalosh regalim, when all came to the Mikdash, the entire nation absorbed this pure awe — the word "yei'ra'eh" itself hints at "yirah," fear.

וע"ז אנו מבקשים ושם נעבדך ביראה.

And concerning this we pray, "And there we will serve You with awe."

Our tefillah for the rebuilt Mikdash is a request to once again attain that pure yirah in Hashem's service.

וכ"כ על אהרן ואתנם לו מורא וייראני כו'.

And so it is written of Aharon: "I gave them to him [as] awe, and he feared Me" (Malachi 2:5).

Aharon embodied this trait — Hashem granted him awe, and he stood in fear before Him.

והנה בזוה"ק יתרו איתא כי עיקר השלימות הוא ליראי ה' כמ"ש אין מחסור ליראיו.

And behold, in the holy Zohar (Yisro) it is stated that the essence of perfection belongs to those who fear Hashem, as it says, "There is no lack to those who fear Him" (Tehillim 34:10).

True shleimus (wholeness) is reserved for those who possess yiras Hashem — for the God-fearing lack nothing.

ממשמע דאין מחסור שלום איקרי ע"ש.

From the implication of "there is no lack," it is called "shalom (peace/wholeness)" — see there.

"No lack" is precisely the definition of shalom, which denotes completeness with nothing missing.

ולכן זכה אהרן למדת השלום אוהב ורודף שלום.

Therefore Aharon merited the trait of shalom — "loving peace and pursuing peace."

Because Aharon possessed pure yirah, he attained the wholeness of shalom and became its great lover and pursuer.

כי שלום שמו של הקב"ה.

For "Shalom" is the Name of the Holy One.

Shalom is itself one of Hashem's Names, so attaining shalom means cleaving to Him.

ולפי שחל עליו יראת ה' טהורה לכן זכה אל השלום.

And because the pure fear of Hashem rested upon him, therefore he merited shalom.

The pure yirah and shalom are linked: the former is the gateway to the latter.

ומה"ט נקרא עיר הקודש ירושלים על היראה והשלימות שנמצא בה.

And for this reason the holy city is called Yerushalayim, on account of the yirah and the shleimus found within it.

The very name Yerushalayim weaves together yirah (awe) and shalom/shaleim (wholeness) — the two qualities the city embodies.

וגם בש"ק דחל יראת ה' על בנ"י כדאיתא אפי' ע"ה אימת שבת עליו לכן נק' שלום.

And also on the holy Shabbos, when the fear of Hashem rests upon Bnei Yisrael — as it is stated, "Even an am ha'aretz (unlearned person) has the awe of Shabbos upon him" — therefore [Shabbos] is called shalom.

Shabbos too brings an awe of Hashem upon every Jew, even the simplest; and because of that yirah, Shabbos itself bears the name Shalom.

וזה רמז המד' ממתים ידך ה'.

And this is the hint of the Midrash, "From men, by Your hand, Hashem."

The verse expounded at the outset alludes to this whole theme of Aharon's portion granted directly by Hashem's hand.

שזכה אהרן אל השלימות והתמימות בכח שמו ית' ע"י העבודה ששרת לפניו במקדש אני חלקך כו' לכן חלקו בחיים.

That Aharon merited the wholeness and the perfect simplicity through the power of His Name, by means of the avodah with which he served before Him in the Mikdash — "I am your portion" — therefore his portion is in life.

Through his service in the Mikdash, Aharon was bound to Hashem's own Name; since "Hashem is his portion," his share is in true, eternal life.

ולנפש לא יטמא.

"And he shall not become impure for a [dead] soul" (Vayikra 21:1).

The kohen's separation from death's impurity reflects that his portion lies entirely in life and purity.

וזכה לטהרה לו ולכל בנ"י כי כל הטהרה של בנ"י נמסרה ביד הכהן.

And he merited taharah (purity) for himself and for all Bnei Yisrael, for all the purity of Bnei Yisrael was placed in the hand of the kohen.

Aharon is not only personally pure; he is the channel through whom the purity of the entire nation is administered.

והנה כתי' תורת ה' תמימה כו' עדות ה' כו' והם ו' מדרגות.

And behold, it is written, "The Torah of Hashem is perfect... the testimony of Hashem [is faithful]..." — and these are six levels (Tehillim 19:8-10).

The verses in Tehillim enumerate six praises of Hashem's Torah, corresponding to six spiritual rungs.

ויראת ה' טהורה היא מדרגת אהרן כידוע.

And "the fear of Hashem is pure" is the level of Aharon, as is known.

Among those six, the rung of "yiras Hashem tehorah" — pure fear — is specifically Aharon's portion.

וזה תכלית הטהרה כי כל המידות צריכין לטהר כמו שניתן ימי הספירה לזכות לטהר על ידה כל המידות.

And this is the goal of purity, for all the middos (character traits) must be purified — just as the days of Sefirah were given to merit, through them, the purification of all the middos.

Pure yirah is the culmination of all purification; the Sefiras HaOmer is precisely the time given to refine every one of one's middos.

שבע שבתות תמימות.

"Seven complete weeks" (Vayikra 23:15).

The seven weeks of the Omer correspond to refining the seven core middos until they are "complete."

כענין שנאמר כל דבר אשר יבא באש תעבירו באש כו' וכן במים וכן בכל המידות.

Similar to what is said, "Every thing that comes into the fire you shall pass through the fire... and so in water" (Bamidbar 31:23) — and so too with all the middos.

Just as vessels are purged by fire and water according to their nature, each character trait must be passed through its own process of purification.

ומדתו של אהרן הוא שורש הטהרה ועיקרה.

And the trait of Aharon is the root and essence of purity.

Aharon's pure yirah is the very source from which all purification flows.

לכן עיקר הטהרה היא במדה זו ובל"ג בעומר ושאר הטהרה נגמרה ממילא.

Therefore the essence of purification is in this trait, and on Lag BaOmer, and the rest of the purification is completed automatically.

Once the root-trait of pure yirah is purified — which the Sefas Emes associates with Lag BaOmer — the refinement of the remaining middos follows of itself.

וכל טהרת העומר היא ג"כ ע"י הכהן שהניף העומר.

And all the purification of the Omer is likewise through the kohen, who waved the Omer offering.

Even the purifying power of the Omer days comes by way of the kohen, who performs the waving — again pointing to Aharon as the conduit of purity.

ושמעתי מפי מו"ז ז"ל כי בל"ג בעומר יכולין לזכות ליראת ה'.

And I heard from the mouth of my grandfather, of blessed memory, that on Lag BaOmer one can merit yiras Hashem.

The Sefas Emes cites a teaching from his grandfather (the Chiddushei HaRim) that Lag BaOmer is an auspicious time to attain the fear of Hashem.

ואפשר שהוא מטעם הנ"ל שאהרן הכהן מסייע במדת יראת ה' טהורה כמ"ש:

And it is possible that this is for the reason mentioned above — that Aharon the Kohen assists in the trait of the pure fear of Hashem, as explained.

The Sefas Emes suggests that Lag BaOmer's power to grant yirah flows from Aharon, the root of pure yiras Hashem, who lends his aid in attaining this trait.

Summary: Pure yiras Hashem — the awe of His exaltedness rather than dread of punishment — is the level of Aharon HaKohen, who served in the Mikdash like a ministering angel. This fear is the root of all purity and the gateway to shalom, the Name of Hashem and the quality of "lacking nothing." Yerushalayim and Shabbos both carry this fusion of awe and wholeness. The seven weeks of the Omer purify all the middos, but their root is Aharon's pure yirah; hence, as the Sefas Emes heard from his grandfather, Lag BaOmer is an auspicious time to attain yiras Hashem through Aharon's aid.