Shevuot 13B

כרת דיממא לרבי לית ליה.

It must be that R' Yehuda HaNasi concedes that Yom Kippur does not atone for one who violates the day itself and does not repent, as if you do not say so, according to R' Yehuda HaNasi, there would be no instance in which a person would be liable to receive karet for violating Yom Kippur in the daytime.

אלמה לא? משכחת לה דאכל אומצא וחנקיה ומית; אי נמי דאכל סמוך לשקיעת החמה ⁠– דלא הוה שהות לכפורי ליה!

The Talmud questions this proof: Why not? You could find it in a case where he ate a piece of meat, and while he was eating it choked him and he died, or in a case where he ate immediately before sunset at the end of the day. Even if one holds that Yom Kippur does atone for violations of the day itself, in these cases it could not, as there was no time after the violation for the day to atone for him, in the first case because he was already dead, and in the second case because it was no longer Yom Kippur.

אחד ישראל ואחד כהנים ואחד כהן משוח.

§ The Mishnah (2b) states: Israelites and priests and the anointed priest, i.e., the High Priest, equally achieve atonement. What is the difference between Israelites, priests, and the anointed priest? The difference is only that the priests achieve atonement for their defiling of the Temple or its sacrificial foods through the bull that the High Priest offers on Yom Kippur, whereas the Israelites achieve atonement for their transgressions through the goats that are sacrificed on Yom Kippur.

הא גופא קשיא ⁠– קתני: אחד ישראל ואחד כהנים ואחד כהן משוח; והדר תני: מה בין ישראל לכהנים ולכהן משוח! אמר רב יהודה, הכי קאמר: אחד ישראל ואחד כהנים ואחד כהן משוח מתכפרין בשעיר המשתלח בשאר עבירות, ואין חילוק ביניהן. ומה בין ישראל לכהנים ולכהן משוח? אלא שהפר מכפר על הכהנים על טומאת מקדש וקדשיו וכו׳.

The Talmud asks: This Mishnah itself is difficult, as it teaches: Both Israelites and priests and the anointed priest equally achieve atonement. But then it teaches: What is the difference between Israelites, priests, and the anointed priest? Rav Yehuda said that this is what the Mishnah is saying: Both Israelites and priests and the anointed priest equally achieve atonement through the scapegoat for transgressions other than the defiling of the Temple or its sacrificial foods, and in this regard there is no distinction between them. But what is the difference between Israelites, priests, and the anointed priest? The difference is only that the bull of the High Priest that he offers on Yom Kippur atones for the priests for their defiling of the Temple or its sacrificial foods, whereas the Israelites achieve atonement for their transgressions through the goats that are sacrificed on Yom Kippur.