הא אינו נושא אלא עון טומאה שהותרה מכללה בציבור וקשיא לרב ששת תנאי היא דתניא ציץ בין שישנו על מצחו בין שאינו על מצחו מרצה דברי רבי שמעון

Apparently, the frontplate gains forgiveness only for the sin of impurity, which was exempted from its general prohibition in cases involving the public. This poses a difficulty to the opinion of Rav Sheshet, who said that the prohibition of impurity is overridden in cases involving the public, as the baraita clearly states that impurity is permitted. The Gemara responds: According to Rav Sheshet, the question of whether the prohibition of impurity is permitted or overridden in cases involving the public is the subject of a dispute between tanna’im, as it was taught in a baraita:

The frontplate effects acceptance whether it is on the High Priest’s forehead or whether it is not on the High Priest’s forehead when the offering becomes impure. This is the statement of Rabbi Shimon.

רבי יהודה אומר עודהו על מצחו מרצה אין עודהו על מצחו אינו מרצה אמר לו רבי שמעון כהן גדול ביום הכפורים יוכיח שאין עודהו על מצחו ומרצה

Rabbi Yehuda says: As long as it is on his forehead it effects acceptance; if it is no longer on his forehead it does not effect acceptance. Rabbi Shimon said to Rabbi Yehuda: The case of the High Priest on Yom Kippur can prove that your statement is incorrect, as on Yom Kippur when the High priest wears only four linen garments the frontplate is no longer on his forehead, and it still effects acceptance.

אמר לו רבי יהודה הנח לכהן גדול ביום הכפורים שטומאה הותרה לו בציבור מכלל דרבי שמעון סבר טומאה דחויה היא בציבור

Rabbi Yehuda said to him: Leave the case of the High Priest on Yom Kippur, as the atonement of the frontplate is unnecessary because the prohibition of performing the Temple service in impurity is permitted in cases involving the public. Learn by inference that Rabbi Shimon holds that impurity is overridden in cases involving the public, and that is why the atonement of the frontplate is necessary. The dispute between Rav Sheshet and Rav Naḥman is based on a tannaitic dispute, and the baraita cited above is in accordance with the opinion of Rabbi Yehuda.

אמר אביי בנשבר הציץ דכולי עלמא לא פליגי דלא מרצה כי פליגי דתלי בסיכתא רבי יהודה סבר על מצח ונשא

The Gemara proceeds to analyze the tannaitic dispute between Rabbi Shimon and Rabbi Yehuda. Abaye said: In a case where the frontplate broke, everyone, including Rabbi Shimon, agrees that the frontplate no longer effects acceptance. When they disagree is in a case where the frontplate is not on his forehead but is hanging on a peg. Rabbi Yehuda holds that the verse: “ And it shall be on the forehead of Aaron and Aaron shall gain forgiveness for the sin committed in the sacred things” (Exodus 28:38) means that the frontplate atones for sin as long as it is on his forehead.

ורבי שמעון סבר תמיד לרצון לפני ה׳ מאי תמיד אילימא תמיד על מצחו מי משכחת לה מי לא בעי מיעל לבית הכסא ומי לא בעי מינם אלא תמיד מרצה הוא

And Rabbi Shimon holds that emphasis should be placed on the end of that verse: “ It shall be always upon his forehead that they may be accepted before the Lord. ” From this, Rabbi Shimon derived that the frontplate always effects acceptance, even when it is not upon the High Priest’s forehead, as what is the meaning of the word always in the verse? If we say that it means that the frontplate must always be on the High Priest’s forehead, do you find that situation in reality? Doesn’t he need to enter the bathroom, when he must remove the frontplate bearing the name of God? Similarly, doesn’t he need to sleep, at which time he removes the priestly vestments? Rather, it means that the frontplate always effects acceptance, whether or not it is on his forehead.

ולרבי יהודה נמי הא כתיב תמיד ההוא תמיד שלא יסיח דעתו ממנו כדרבה בר רב הונא דאמר רבה בר רב הונא חייב אדם למשמש בתפיליו בכל שעה ושעה קל וחומר מציץ

The Gemara asks: And according to Rabbi Yehuda as well, isn’t it written: “ Always”? Clearly it does not mean that the frontplate must always be on his forehead. The Gemara answers: That term:“ Always, ” teaches that the High Priest must always be aware that the frontplate is on his head, and that he should not be distracted from it. This is in accordance with the statement of Rabba bar Rav Huna, as Rabba bar Rav Huna said: A person must touch the phylacteries on his head and on his arm each and every hour, to maintain awareness of their presence. This is derived by means of an a fortiori inference from the frontplate: