Three channels of sanctifying Hashem

וכתיב ונקדשתי בתוך בנ"י.

And it is written: "And I shall be sanctified in the midst of Bnei Yisrael."

The Sefas Emes opens with the pasuk that the sanctification of Hashem's Name takes place specifically within Klal Yisrael, for they are the vessel through which His kedushah is revealed in the world.

כי בנ"י הם כלים לקבל הקדושה.

For Bnei Yisrael are the vessels fit to receive the kedushah.

Klal Yisrael is not merely a recipient of holiness but a prepared keli (vessel) — by their very nature they are built to absorb and contain the kedushah of Hashem.

והנה מי שמוסר נפשו בפועל רמש נעשה גופו קדוש.

Now, one who actually gives over his life — in deed — his very body becomes holy.

Mesirus nefesh (self-sacrifice) carried out in action sanctifies even the physical body, drawing kedushah down into the realm of the deed.

וכמו כן יש בבחי' דיבור ומחשבה.

And likewise there is an aspect of this in speech and in thought.

The same power of self-sacrifice can be expressed not only through deed but also on the levels of dibur (speech) and machshavah (thought), each sanctifying its own dimension of a person.

כדאיתא בספרים מי שחושב תמיד למסור נפשו לה' מתקדשין מחשבותיו.

As it is brought in the sefarim: one who constantly thinks of giving over his life to Hashem — his thoughts become sanctified.

Even without a physical act, the steady inner resolve to be moser nefesh for Hashem brings kedushah to the faculty of thought.

וכמו כן בדיבור כשאומרין ה' אחד ואהבת כו' בכל נפשך זוכין לקדושת הדיבור.

And so too in speech: when one says "Hashem is One" and "you shall love… with all your soul," one merits the kedushah of speech.

Reciting the Shema and accepting to love Hashem "with all your soul" — to the point of giving up one's life — sanctifies the power of dibur itself.

וג' בחי' הנ"ל הם כהן לוי ישראל.

And these three aspects mentioned above correspond to Kohen, Levi, and Yisrael.

The three channels of sanctification — deed, speech, and thought — map onto the three groups within Klal Yisrael, each one a vehicle for a different mode of kedushah.

והכהן נתקדש גם בעובדא ולוים בשיר וישראל במחשבה:

The Kohen is sanctified also through deed (the avodah), the Leviim through song, and Yisrael through thought.

The Kohen's kedushah comes through the physical avodah of the korbanos, the Levi's through the song of the Beis Hamikdash (speech), and the Yisrael's through machshavah — together the three modes of mesirus nefesh are realized in Klal Yisrael.

Summary: Hashem is sanctified within Bnei Yisrael, who are the vessels for His kedushah. Mesirus nefesh can be expressed on three levels — deed, speech, and thought — and these three correspond to Kohen, Levi, and Yisrael, who each draw down holiness through their own avodah.