Yoma 8A

ומה ציץ, שאין בו אלא אזכרה אחת, אמרה תורה: ״על מצחו תמיד״⁠ — שלא יסיח דעתו ממנו. תפילין שיש בהן אזכרות הרבה ⁠— על אחת כמה וכמה.

Just as with regard to the frontplate, which has only one mention of God’s name, the Torah said: “It should be always upon his forehead,” teaching that that he should not be distracted from it, with regard to tefillin, which have numerous mentions of God’s name in their 4 passages from the Torah, all the more so one may not be distracted from them.

ולרבי שמעון דאמר תמיד מרצה, והא כתיב ״על מצחו ונשא״! ההוא לקבוע לו מקום הוא דאתא.

The Talmud asks: And according to R' Shimon, who says that the verse: “It should be always upon his forehead,” teaches that the frontplate effects acceptance even when it is not on the High Priest’s forehead, isn’t it also written: “On his forehead…and should gain forgiveness”? The Talmud answers: That verse comes to establish the place where the High Priest should position the frontplate, not to indicate that it effects acceptance only when it is on his forehead.

ורבי יהודה לקבוע לו מקום מנא ליה? נפקא ליה מ״על מצחו״. ורבי שמעון נמי, תיפוק ליה מ״על מצחו״? אין הכי נמי.

The Talmud asks: And according to R' Yehuda, from where does he derive the halakha to establish the frontplate’s place on the High Priest’s forehead? The Talmud answers: He derives it from that which is written: “On his forehead.” The Talmud asks: And R' Shimon, too, let him derive the placement of the frontplate from: “On his forehead.” The Talmud responds: Yes, it is indeed so; that is R' Shimon’s source.

אלא, ״על מצחו ונשא״ מאי עביד ליה? אמר לך: ראוי למצח מרצה, שאינו ראוי למצח אינו מרצה. לאפוקי נשבר הציץ, דלא מרצה.

The Talmud asks: Rather, if so, with regard to the verse: “On his forehead…and should gain forgiveness,” what does R' Shimon do with that verse? The Talmud responds that R' Shimon could have said to you: The frontplate that is intact and fit for placement on the High Priest’s forehead effects acceptance; that which is not fit for placement on the High Priest’s forehead does not effect acceptance. This comes to exclude a case where the frontplate broke, in which case it does not effect acceptance.