The sukkah as Mikdash and gatherer of Israel

סוכות זמן שמחתינו.

Sukkos is "the time of our rejoicing."

The Sefas Emes opens with the defining quality of Sukkos — it is z'man simchaseinu, the festival of joy.

דכ' שמחתי באומרים כו' בית ה' נלך.

As it is written, "I rejoiced when they said to me, 'Let us go to the House of Hashem.'" (Tehillim 122:1)

The joy of Sukkos is the joy of going toward the Bais Hashem — the House of Hashem.

וסוכה הארה מביהמ"ק.

And the sukkah is an illumination from the Bais HaMikdash.

The sukkah carries within it a ray of the light of the Bais Hamikdash; dwelling in it is a taste of being in Hashem's House.

וגם היא בית ה' שחל שם שמים על הסוכה.

And it too is a "House of Hashem," for the Name of Heaven rests upon the sukkah.

Because Hashem's Name rests upon it, the sukkah is itself a "Bais Hashem" — a dwelling imbued with Divine presence.

והגם שיש לנו להתעצב בחורבן בית המקדש גם בדוד המע"ה דרשו כשאמרו לו מתי ימות ויבנה ביהמ"ק שמח.

And although we have cause to be saddened over the destruction of the Bais HaMikdash — even of David HaMelech they expounded that when they told him "when will you die and the Bais HaMikdash be built," he rejoiced —

The sukkah's link to the Mikdash could stir grief over the churban; yet Chazal teach that David, hearing that the Mikdash would only be built after his death, still rejoiced — finding joy in the future Beis Hamikdash rather than sorrow.

כמו כן אעפ"י כשנזכרין ביהמ"ק אנו נעצבין אעפ"י כן שמחים בזה שכבר זכו אבותינו להיות בביהמ"ק וגם אנו עתידין להיות עוד בביהמ"ק.

So too, even though when we recall the Bais HaMikdash we become saddened, nevertheless we rejoice in this — that our forefathers already merited to be in the Bais HaMikdash, and we too are destined to be in the Bais HaMikdash again.

Like David, we hold both feelings together: sorrow at the loss, yet joy that the Avos stood in the Mikdash and that we ourselves will yet stand there in the future geulah.

לכן כשיש זכר מביהמ"ק אנו שמחים.

Therefore, when there is a remembrance of the Bais HaMikdash, we rejoice.

The sukkah, as a "remembrance" of the Mikdash, is thus a cause for joy and not only for grief — which is why Sukkos is z'man simchaseinu.

עומדות היו רגלינו כו' כעיר שחוברה לה יחדיו.

"Our feet were standing… like a city that is joined together." (Tehillim 122:2-3)

The Sefas Emes now turns to Yerushalayim as "a city joined together" — a place of unity — to illuminate the gathering quality of the sukkah.

איתא בירושלמי דחגיגה עיר שכל ישראל נעשין כאיש אחד בתוכה.

It is brought in the Yerushalmi of Chagigah: a city in which all of Yisrael become as one man within it.

The Yerushalmi explains "a city joined together" to mean Yerushalayim unites all of Bnei Yisrael into a single being — a place of total achdus.

וגם הסוכה מאסף כל בנ"י כעין ירושלים.

And the sukkah too gathers all of Bnei Yisrael, similar to Yerushalayim.

The sukkah shares this unifying power of Yerushalayim — it draws all of Bnei Yisrael together into one.

כמ"ש כל האזרח כו' ישבו ראוין כל ישראל לישב בסוכה אחת:

As it is written, "every citizen [in Yisrael] shall dwell [in sukkos]" (Vayikra 23:42) — [from which Chazal derive that] all of Yisrael are fit to dwell in a single sukkah.

From the wording "every citizen shall dwell," Chazal learn that in principle all of Klal Yisrael could sit together in one sukkah — expressing the sukkah's essence as a gatherer of the entire nation into a unity, like Yerushalayim itself.

Summary: Sukkos is the time of joy because the sukkah is an illumination of the Bais Hamikdash, a "House of Hashem" upon which His Name rests. Though remembering the Mikdash could bring sorrow over the churban, we follow David HaMelech in rejoicing — that our forefathers stood in the Mikdash and that we will yet return to it. Like Yerushalayim, "the city joined together," the sukkah gathers all of Bnei Yisrael into one, for in principle all of Yisrael are fit to dwell in a single sukkah.