Shavuos as Ingathering Through Torah

בענין מה שנקרא חג השבועות עצרת בדברי חכמים.

Concerning why Chag HaShavuos is called "Atzeres" in the words of the Chachamim.

The Sefas Emes asks why Chazal refer to Shavuos by the name Atzeres, a word connoting gathering and restraint.

דכתיב תורה צוה לנו משה כו' קהלת יעקב.

As it is written: "Moshe commanded us the Torah… the heritage of the congregation (kehillas) of Yaakov" (Devarim 33:4).

The passuk links the Torah to the "congregation of Yaakov," tying the giving of Torah to Bnei Yisrael becoming one assembled kehillah.

וכך הוא בימי הספירה נעשין בנ"י קהלה אחת וזוכין אח"כ לתורה בשבועות כאשר אמר אמו"ז ז"ל כי ימי ספירת העומר הוא ע"ש קיבוץ כללות בנ"י וזה הי' מתקיים בהקרבת העומר וכשהיו בנ"י בשלימות הראוי.

And so it is: during the days of Sefirah, Bnei Yisrael become one congregation, and afterward they merit the Torah on Shavuos — as my grandfather and teacher, of blessed memory, said, that the days of Sefiras HaOmer are named for the gathering-together of the totality of Bnei Yisrael; and this was fulfilled through the offering of the Omer, when Bnei Yisrael were in their proper wholeness.

The Sefiras HaOmer is a process of unification: over these days the nation binds together into a single body, and only such a unified people is fit to receive the Torah. In the times of the Mikdash the Korban HaOmer accomplished this when Bnei Yisrael stood whole.

אבל עתה שאנו במדריגה פחותה צריכין עכ"פ לקבל זה ההתכללות ע"י התורה כי גם נכלל בפסוק שע"י התורה מורשה קהלת יעקב.

But now, when we are on a lower level, we must at least receive this inclusion (hiskallelus) by means of the Torah — for this too is contained in the passuk: that through the Torah it becomes "the heritage of the congregation of Yaakov."

Lacking the Mikdash and the Omer, we attain the same unity through the Torah itself, which gathers Bnei Yisrael into one congregation when it is received as their shared inheritance.

ועצרת הוא כנופיא לכן קראוהו חז"ל עצרת כנ"ל:

And "Atzeres" means a gathering (kenufya); therefore Chazal called it Atzeres, as above.

Because the essence of the day is the gathering of Bnei Yisrael into one assembly through the Torah, Chazal gave it the name Atzeres — the day of ingathering.

Summary: Shavuos is called Atzeres because its essence is the ingathering of Bnei Yisrael into one congregation. The days of Sefiras HaOmer unify the nation so that they are fit to receive the Torah, and the Torah — "the heritage of the congregation of Yaakov" — is itself the force that binds them into one. In the days of the Mikdash this unity came through the Korban HaOmer; nowadays we attain that same hiskallelus through the Torah, and so the day bears the name Atzeres, a gathering.