Mitzvos that sanctify the whole day

את משפטי תעשו כו' ללכת בהם.

"My ordinances you shall perform... to walk in them" (Vayikra 18:4).

The Sefas Emes begins from the passuk's phrase "to walk in them," which implies an ongoing movement within the mitzvos, not merely a single act of performance.

ואח"כ כחי' אשר יעשה כו' האדם וחי בהם.

And afterward, as in the verse "which a man shall do... and live by them" (Vayikra 18:5).

He pairs this with the next passuk, which speaks of doing the mitzvos and deriving life from them — two complementary phrases he will now explain.

פרשנו כי המצות נותנין קדושה ודביקות לפניהם ולאחריהם.

We have explained that the mitzvos grant holiness and dveikus (attachment) both before them and after them.

A mitzvah is not confined to the moment of its performance; its kedushah radiates backward into the anticipation that precedes it and forward into the time that follows it.

וצריך האדם להתדבק במצוה ע"ד ללכת בה כל היום.

And a person must cleave to the mitzvah in the sense of "walking in it" all day long.

"To walk in them" means to carry the connection to the mitzvah throughout the entire day, so that one's whole life moves within it.

וכשעושה המצות ע"ד זה שישאר בו חיות מן המצוה כל היום כמ"ש ומצותי תצפון אתך.

And when one performs the mitzvos in this way, the vitality of the mitzvah remains within him the whole day, as it is written, "and store My mitzvos with you" (Mishlei 2:1).

By performing a mitzvah with the intent that its life-force endure, a person "stores up" the mitzvah within himself, so that its energy stays with him long after the act.

וכמו כן קודם המצוה להיות משתוקק כל היום לעשות מצות ה' והכנה זו כל היום אל המצוה נותן לאדם חיות.

And likewise before the mitzvah, to yearn all day to perform Hashem's mitzvos; and this preparation all day toward the mitzvah grants a person vitality.

The same is true on the "before" side: a day-long longing and readiness to do Hashem's will is itself a source of chiyus (life-force), even before the deed is done.

לכן כתי' אשר יעשה לשון עתיד.

Therefore it is written "asher ya'aseh" (which he shall do) — in the future tense.

The passuk deliberately uses the future tense to teach that life is drawn even from the mitzvah one is still about to perform.

וחי בהם גם קודם העשי'.

"And live by them" — even before the doing.

One already "lives by them" through the anticipation and preparation, before the mitzvah is actually carried out.

כי המצות הם עצות להתדבק בהשי"ת.

For the mitzvos are "eitzos" (counsels/means) to cleave to Hashem.

The Sefas Emes plays on "mitzvos"/"eitzos": the commandments are really Divine strategies whose whole purpose is to bring a person into dveikus with Hashem.

והוא בעובדא ומעשה כדי להתקדש ע"י המצוה כל המעשים כענין שאמרו כל שהי' בכלל ויצא מן הכלל ללמד על הכלל כולו יצא.

And this is through deed and action, so that through the mitzvah all of one's actions become sanctified — like the principle they stated: "Anything that was included in a general rule but was singled out, is singled out not [only] for itself but to teach about the entire general category."

A single mitzvah-act, though it is one specific deed "singled out" from all one's activities, comes to sanctify the whole range of one's actions, just as in the hermeneutic rule a singled-out case illuminates the entire class.

וכן צריך להיות רצון האדם שע"י המצוה יתקן כל המעשים כי היד המנחת תפילין מתקדשת בכל הפעולות שנעשה ע"י הידים.

So too a person's ratzon (will) should be that through the mitzvah all his deeds be rectified — for the hand that lays tefillin becomes sanctified in all the actions performed by the hands.

One should consciously intend that a mitzvah elevate everything: the hand that dons tefillin is meant to carry that sanctity into every act it later performs.

וכן הוא בכל המצות.

And so it is with all the mitzvos.

This principle is not unique to tefillin; every mitzvah radiates its holiness outward into the rest of a person's deeds.

זה ללכת בהם:

This is [the meaning of] "to walk in them."

To "walk in" the mitzvos is precisely this: to let each mitzvah's holiness extend before and after it, sanctifying one's entire daily walk through life.

Summary: A mitzvah is not limited to the instant of its performance. Through yearning beforehand and lingering vitality afterward, its kedushah and dveikus extend across the whole day — this is what "to walk in them" means. The mitzvos are really eitzos, counsels for cleaving to Hashem, and a person should intend that each single mitzvah sanctify the entire range of his actions, as the hand that lays tefillin sanctifies all that the hands do.