Shevuot 9A

אלא אחת בשנה.

only once a year.

ולרבי ישמעאל דאמר אין בה ידיעה בתחלה ויש בה ידיעה בסוף בר קרבן הוא, שעיר הנעשה בחוץ אמאי מכפר? על שאין בה ידיעה לא בתחלה ולא בסוף.

According to the Mishnah, the external goat atones for a case in which there was no awareness at the beginning but there was awareness at the end. The Talmud asks: And according to R' Yishmael, who says: For a case in which one did not have awareness at the beginning but did have awareness at the end, that person is liable to bring an offering, for what does the goat whose blood presentation is performed outside the Sanctuary atone? The Talmud answers: It atones for a case in which one did not have awareness, neither in the beginning, nor in the end.

האי שעירי הרגלים ושעירי ראשי חדשים מכפרין! סבר לה כרבי מאיר, דאמר: כל השעירים כפרתן שוה ⁠– על טומאת מקדש וקדשיו.

The Talmud challenges this answer: But for that case, the goats of the Festivals and the goats of the New Moons atone. The Talmud explains: He holds in accordance with the opinion of R' Meir, who says: The atonement effected by all the goats offered as part the additional offerings, i.e., those of the New Moons, the Festivals, and Yom Kippur, is the same: They all atone for various cases of the defiling of the Temple or its sacrificial foods.

אלא למאי הלכתא איתקש חיצון לפנימי? מה פנימי אינו מכפר בשאר עבירות, אף חיצון אינו מכפר בשאר עבירות.

The Talmud asks: But if R' Yishmael holds that the internal goat atones for a situation in which there was no awareness at all, with regard to what halakha does the Torah juxtapose the internal goat with the external goat? The Talmud explains: The juxtaposition teaches that just as the internal goat does not atone for other transgressions, so too, the external goat does not atone for other transgressions. Rather, they both atone only for the defiling of the Temple or its sacrificial foods.