Unity sealed by Shemini Atzeres

ביום השמיני עצרת תהי' לכם כנופיא.

"On the eighth day there shall be an atzeres (assembly) for you" — a gathering.

The Sefas Emes opens by noting that Shemini Atzeres is described as a "kenufya," a gathering, hinting that its essence is the drawing together of Bnei Yisrael into one.

כי סוכות חג האסיף ובנ"י שכנסי' שלהם לשם שמים כדי שיחול שם שמים על הסוכה לכן סופה להתקיים ונשאר להם האחדות.

For Sukkos is the festival of the ingathering, and since the assembling of Bnei Yisrael is l'sheim Shomayim (for the sake of Heaven), so that the Name of Heaven should rest upon the sukkah, therefore it is destined to endure, and the achdus (unity) remains with them.

Sukkos is the time of ingathering, and because Bnei Yisrael gather purely for Hashem's sake — so that His Presence rests on the sukkah — that unity is not a passing thing but takes on permanence.

ז"ש עצרת תהי' לכם להיות נשאר בהאחדות.

This is the meaning of "atzeres shall be for you" — that the unity should remain.

The word "atzeres" implies holding fast and retaining; Shemini Atzeres is meant to lock in the achdus achieved over the festival.

וכן בכל כנסי' כך הפי' אם מתכנסין לשם שמים נשאר קיים אפילו כשכל אחד הולך לביתו.

And so it is with every gathering: this is the meaning — that if people assemble l'sheim Shomayim, it remains enduring even when each one returns to his home.

The same principle applies to any coming-together of Yidden: when the gathering is for Hashem's sake, the bond it forges outlasts the gathering itself and stays intact even after everyone disperses.

וכמו בשבת קודש מתאחדין.

Just as on Shabbos Kodesh we become unified.

Shabbos too is a time when Bnei Yisrael are drawn into oneness.

ואם הוא לש"ש סופה להתקיים גם בימי המעשה.

And if it is l'sheim Shomayim, it is destined to endure even into the weekdays.

The holiness and unity of Shabbos, when entered into for Heaven's sake, carry over and sustain a person through the ordinary workdays that follow.

וכן האחדות מן הסוכות הולך עמנו גם לבית:

So too the achdus drawn from Sukkos goes along with us even into the home.

The oneness gathered under the sukkah is not left behind at the festival's end; it accompanies us back into our homes and everyday lives.

Summary: Shemini Atzeres, the "gathering," seals the unity of Bnei Yisrael achieved on Sukkos. Because that gathering is purely l'sheim Shomayim, drawing Hashem's Presence upon the sukkah, the achdus becomes permanent — like the holiness of Shabbos, it accompanies us home and into the weekdays that follow.