Accepting Kingship Before Mitzvos
בפרשת והי' אם שמוע לא נזכר בכל מאודכם
In the parsha of "Vehayah im shamo'a" (the second paragraph of Shema), the phrase "with all your might" (b'chol me'odecha) is not mentioned.
The Sfas Emes notes that unlike the first paragraph of Shema, which says to love Hashem "with all your might," this phrase is conspicuously absent from the second paragraph.
והענין כמ"ש ז"ל מקודם יקבל עליו עול מלכות
The matter is as Chazal have said: first a person accepts upon himself the yoke of the Kingship of Heaven (ol malchus Shamayim),
He resolves this by invoking the teaching of Chazal that the sequence in Shema reflects a deliberate order: one first takes on the yoke of accepting Hashem as King.
אח"כ עול מצות
and afterward the yoke of the mitzvos (ol mitzvos).
Only after accepting His Kingship does one take on the yoke of performing the mitzvos.
דקבלת מלכותו צריך להיות בכל מה שיצוה אותנו כמ"ש נעשה ונשמע
For the acceptance of His Kingship must extend to whatever He commands us, as it is written, "Na'aseh v'nishma" — "We will do and we will listen" (Shemos 24:7).
Accepting Hashem's Kingship means total readiness to do whatever He asks, which is the essence of Bnei Yisrael's declaration of "Na'aseh v'nishma" at Har Sinai.
(ונעשה) [*ונשמע] אם יהי' רצונו ית' שלא לעשות עניני עוה"ז כלום וקבלה זו הכנה (לנשמע) [*לנעשה] שהוא בסדר שניתן לנו בעוה"ז בחי' המצות שתלוין בעניני עוה"ז דווקא לעשותם ג"כ לש"ש ובזה יש נחת רוח להקב"ה ביותר:
"V'nishma" means that, were it to be Hashem's will that we do nothing whatsoever with the affairs of this world, we would heed Him; and this acceptance is the preparation for "na'aseh" — for the order that has been given to us in this world is the aspect of the mitzvos that depend specifically upon the matters of this world, that we are to perform them too for the sake of Heaven (l'shem Shamayim), and in this there is the greatest nachas ruach to the Holy One, Blessed is He.
"V'nishma" expresses a bittul so complete that one would gladly withdraw entirely from worldly matters if that were Hashem's will; yet that very surrender prepares a person to fulfill "na'aseh" — to engage the physical world through the mitzvos bound up in it, doing so purely for the sake of Heaven, which brings Hashem the greatest delight.
Summary: The Sfas Emes asks why "with all your might" appears in the first paragraph of Shema but not in the second. He answers through the teaching of Chazal that the order of Shema is first accepting the yoke of Hashem's Kingship and only afterward the yoke of the mitzvos. Accepting His Kingship demands a total bittul — the readiness expressed in "Na'aseh v'nishma," whereby Bnei Yisrael would forgo all worldly engagement entirely were that Hashem's will. Yet this very surrender of "v'nishma" is precisely the preparation for "na'aseh": Hashem's actual will is that we serve Him through the mitzvos rooted in the affairs of this world, performing even worldly matters for the sake of Heaven. It is davka this avodah within the physical world, born of complete submission, that brings the greatest nachas ruach to the Holy One, Blessed is He.