Wholehearted will completes the mitzvah

מה שמקשין למה מיוחד ענין לקיחת הקרבן פסח לשבת דהי' צריך להיות לעולם בעשור לחודש הן בשבת והן בחול.

There is a difficulty that is raised: why is the matter of taking the korban Pesach singled out to [be commemorated on] Shabbos, when it should always be on the tenth of the month, whether that falls on Shabbos or on a weekday?

The Sefas Emes opens with the well-known question: the taking of the Pesach lamb happened on the tenth of Nissan, yet we commemorate it specifically on Shabbos HaGadol — why tie it to Shabbos rather than to the calendar date?

אבל נראה כי מסתמא כשבחרו החכמים ביום זה יש בו חשיבות מאוד.

But it appears that surely, when the Chachamim chose this day, there is great significance in it.

The very fact that Chazal fixed this commemoration on Shabbos tells us that the connection to Shabbos is essential.

כי הקבלה שקבלו בנ"י מצוה הראשונה בכל לבם נחשב יותר בשמים מקיום המצוה במעשה.

For the acceptance with which Bnei Yisrael accepted this first mitzvah with all their heart is reckoned in Heaven as greater than the fulfillment of the mitzvah in deed.

Their wholehearted readiness to take the lamb — their inner acceptance of the very first mitzvah — counted in Heaven even more than the physical act itself.

כי בודאי במעשה קשה להיות בלי שום חסרון.

For certainly, in the deed it is difficult to be without any deficiency.

Any physical performance of a mitzvah is bound to have some imperfection.

אבל הקבלה והלקיחה הי' בלב שלם לגמרי.

But the acceptance and the taking were with a completely whole heart.

The inner commitment, by contrast, was flawless and complete.

ולאשר כי הי' אז בשבת.

And because it was then on Shabbos.

And it so happened that the tenth of Nissan that year fell on Shabbos.

ושבת הוא יום שביתה שאין בו מעשה ובשבת אין צריך למעשה רק הרצון בלבד ולכן נחשב הקבלה כאלו גמרו כל המעשה בטוב.

And Shabbos is a day of rest (shevisah) in which there is no [creative] action, and on Shabbos one does not need the deed, only the ratzon (will) alone; therefore the acceptance is reckoned as if they had completed the entire deed in goodness.

Because Shabbos is a day of rest where action ceases and only one's inner will operates, their pure-hearted acceptance on that day was credited as a fully completed mitzvah.

והנה עדיין לא נגמר המכוון שהי' להקב"ה בהוציאנו ממצרים להיות שמו הגדול מקודש על ידינו כמו שיהי' לעתיד.

Now, the intent that the Holy One, blessed be He, had in taking us out of Mitzrayim — that His great Name be sanctified through us as it will be in the future — has not yet been completed.

The full purpose of the Exodus, that Hashem's great Name be sanctified through Bnei Yisrael, is still unfinished; it awaits the future redemption.

כי עמלק הרשע בלבל אותנו כמאמר אשר קרך בדרך.

For the wicked Amalek confused us, as it says, "who happened upon you (asher karcha) on the way."

Amalek's attack threw the world's perception into confusion, "cooling off" the awe of Hashem that the Exodus had aroused.

ולכן מצווין לזכור שנאתו כמו שמצווין לזכור יציאת מצרים כי הוא קלקל הדרך.

Therefore we are commanded to remember our hatred of him, just as we are commanded to remember the Exodus from Mitzrayim, for he ruined the "way."

Because Amalek damaged the path that the Exodus had opened, remembering him is paired with remembering the Exodus itself.

אבל הרצון הי' אמת בבנ"י בעת שנאמר משכו ידיכם מע"ז וקחו לכם כו'.

But the ratzon was true in Bnei Yisrael at the time when it was said, "Draw away your hands from avodah zarah and take for yourselves [a lamb]…"

Even though the final goal is unfinished, Bnei Yisrael's inner will at the moment of the first mitzvah — renouncing idolatry and taking the lamb — was genuine and true.

ולכן בטוחים אנו שיהי' לנו אחרית טוב.

And therefore we are confident that we will have a good end.

That true inner will is our guarantee of an ultimately good outcome.

כי הכלל כל מעשה שאדם עושה בלב שלם אף שבמעשה אינו נגמר כראוי בטוח הוא שיהי' לו עוד תיקון ואחרית לטובה.

For the principle is: any deed that a person does with a whole heart, even if in action it was not completed properly, he is assured that it will yet have a tikkun (rectification) and a good end.

Whenever something is begun with full sincerity of heart, even an imperfect outcome is guaranteed eventual completion and a good ending.

ולכן בשבת שהוא מעין עוה"ב יום שכולו שבת יכולין לעורר הרצון שהיה לנו בתחילת קבלת מלכותו כמאמר זכרתי לך חסד נעוריך כו'.

And therefore on Shabbos, which is a foretaste of the World to Come (olam haba), "a day that is entirely Shabbos," we are able to arouse the ratzon that we had at the beginning of our acceptance of His kingship, as it says, "I remember for you the kindness of your youth…"

Since Shabbos is a taste of the world to come, on it we can reawaken that original, pure will with which we first accepted Hashem's malchus — the "kindness of our youth" that Hashem still recalls.

לכן נקרא שבת הגדול ע"ש שמו הגדול שיתקדש במהרה בימינו אמן:

Therefore it is called Shabbos HaGadol (the Great Shabbos), after His great Name, which should be sanctified speedily in our days, Amen.

The name "Shabbos HaGadol" alludes to Hashem's great Name — the very sanctification that began at the Exodus and will be completed in the geulah.

Summary: We commemorate the taking of the korban Pesach on Shabbos HaGadol because that tenth of Nissan fell on Shabbos, the day of pure ratzon without action. Bnei Yisrael's wholehearted acceptance of their first mitzvah was reckoned in Heaven as a completed deed. Though Amalek later confused the world and the full sanctification of Hashem's Name still awaits the geulah, any beginning made with a whole heart is guaranteed a good end. Each Shabbos — a taste of olam haba — we can reawaken that original pure will with which we first accepted Hashem's kingship, and the name "Shabbos HaGadol" points to the great Name that will yet be fully sanctified.