The seal of Yom Kippur and milah

מ"ש לעיל כי יוהכ"פ מיוחד רק לבנ"י.

As was said above, that Yom Kippur is designated for Bnei Yisrael alone.

The Sefas Emes returns to a point he made earlier: the avodah of Yom Kippur belongs uniquely to Bnei Yisrael and is not shared with the other nations.

רמז לדבר בגמ' חק לישראל הוא אימת הוי חוק בגמר דין והגמר דין הוא ביוהכ"פ זמן החותם.

A hint to this is found in the Gemara: "it is a chok (statute) for Yisrael" - when does it become a chok? At the conclusion of the judgment, and the conclusion of the judgment is on Yom Kippur, the time of the sealing.

He brings a proof from Chazal: the verse calls Yom Kippur a chok "for Yisrael," and the Gemara explains that the binding decree is finalized at the gemar din (final verdict), which occurs on Yom Kippur - the time when the judgment is sealed.

וזה רק לבנ"י וע"ז עדות חותם המילה:

And this belongs only to Bnei Yisrael, and the testimony to this is the seal of the milah (circumcision).

The bris milah is the permanent "seal" stamped upon every Jew, and it is precisely this seal that makes the sealing of Yom Kippur belong to Bnei Yisrael in particular.

Summary: Yom Kippur is the time when the year's judgment is finally sealed, an avodah unique to Bnei Yisrael - for the seal of the bris milah marks them as the people upon whom this sealing takes effect.