Our Gemara on Amud Aleph raises a question about a grouping of similar items in a beraisa. There are six cases in total, and they are mostly similar. Yet, interestingly, they are divided into two sets of three cases:

תָּנוּ רַבָּנַן: ״הֲרֵי אַתְּ אִשְׁתִּי״, ״הֲרֵי אַתְּ אֲרוּסָתִי״, ״הֲרֵי אַתְּ קְנוּיָה לִי״ – מְקוּדֶּשֶׁת. ״הֲרֵי אַתְּ שֶׁלִּי״, ״הֲרֵי אַתְּ בִּרְשׁוּתִי״, ״הֲרֵי אַתְּ זְקוּקָה לִי״ – מְקוּדֶּשֶׁת. וְלִיתְנִינְהוּ כּוּלְּהוּ כַּחֲדָא! תַּנָּא תְּלָת תְּלָת, שַׁמְעִינְהוּ וְגַרְסִינְהוּ.

The Sages taught in a baraita that if a man says to a woman: "You are hereby my wife," or: "You are hereby my betrothed," or: "You are hereby acquired to me," then she is betrothed. If he said to her: "You are hereby mine," or: "You are hereby under my authority," or: "You are hereby bound to me," then she is betrothed. The Gemara questions: Since the halakha is the same for both sets of statements, why does the baraita divide these statements into two groups? The Gemara answers: The tanna heard them as two sets of three, and consequently he taught them in that form. He heard each sequence of three cases as a separate halakha from his teachers, and therefore he preserved them as two sets of three.

Sefer Avodas Hagershoni (Vayikra, p. 232) raises a question: Why should the addition of just a couple of extra words lead to this level of questioning? (After all, we can understand that there might be linguistic or stylistic reasons that make a Mishna easier to read or memorize. See Tiferes Yisrael Boaz Arachin 4:1.) Additionally, there's a famous teaching from the Gra (Shnos Eliyahu Peah 1) that every word of Torah is a Mitzvah, so why not add a Mitzvah or two?

Rav Gershon Klibenski provides an answer, suggesting that redundancy without a purpose, even if it is related to Torah, is not truly considered Torah. Yet, the Gemara eventually concedes that the words were indeed redundant. However, this redundancy serves a different purpose. It is important for the student to repeat the teaching exactly as learned (possibly as an aid to memory, or possibly as a way of maintaining the accuracy of the transmission, since the student can’t be certain which elements of the rabbi's teaching hold significance).

This concept brings to mind the story of Hillel and Shammai, whose teachers, Shmaya and Avtalyon, were converts to Judaism and had difficulties pronouncing certain Hebrew words properly. Hillel and Shammai were so committed to preserving their teachers' words verbatim, that they even retained their mispronunciations (See commentary of Rambam Eduyos 1:3). This exemplifies a powerful lesson in how Judaism maintains its fidelity to the oral tradition.