Introduction
The tractate opens with a lexigraphical discussion of the word I have translated festival איד, whether it is spelled with an aleph or an ayin. While today Ashkenazim and Sephardim do not distinguish in pronouncing these letters, originally they were pronounced differently. Jews of Yemenite descent still pronounce the ayin as a guttural letter, closer to the Arabic sound of gh. This is why Aza in Hebrew became Gaza or Amora (and in Sodom and Amora) became Gemorra.
גמ׳ רב ושמואל חד תני אידיהן וחד תני עידיהן
GEMARA. Rav and Shmuel: One taught edehem (with an aleph) while the other taught edehem (with an ayin).
Rav and Shmuel disagree as to the exact word that appears in the Mishnah which I have rendered festivals.
מאן דתני אידיהן לא משתבש ומאן דתני עידיהן לא משתבש.
מאן דתני אידיהן לא משתבש דכתיב (דברים לב, לה) כי קרוב יום אידם
ומאן דתני עידיהן לא משתבש דכתיב (ישעיהו מג, ט) יתנו עידיהם ויצדקו
The one who taught edehem (with an aleph) is not in error while the one who taught edehem (with an ayin) is not in error.
The one who taught edehem (with an aleph) is not in error, as it is written: For the day of their calamity is at hand (Deuteronomy 32:35);
And the one who taught edehem (with an ayin) is not in error, as it is written: Let them bring their witnesses [testimonies] that they may be justified (Isaiah 43:9).
To support both readings in the Mishnah, the Talmud quotes verses that use both words. We should note that the words have different meanings and neither means festivals. Most scholars do not think that the rabbinic word is actually related to the biblical Hebrew. Rather, it comes from a different origin altogether (and is related to the word Ides, as in the Ides of March.) The sugya presents midrash on the biblical word it connects two words that sound the same but originally had different meanings.
ומאן דתני אידיהן מאי טעמא לא תני עידיהן? אמר לך תברא עדיף.
The one who taught edehem (with an aleph) why did he not teach edehem (with an ayin?
He could say: Calamity is preferable.
The one who related the word to Deuteronomy, where it is found with an aleph, chose that verse because there the word has the connotation of calamity. It is as if he says that the festivals of the idolaters are actually calamities.
ומאן דתני עידיהן מאי טעמא לא תני אידיהן אמר לך מאן קא גרים להו תברא עדות שהעידו בעצמן הלכך עדות עדיפא
The one who taught edehem (with an ayin) why did he not teach edehem (with an aleph)?
He might say: What is it that brings about that calamity? The testimony they testify about themselves. Therefore testimony is preferable.
The reading of the word with an ayin connects it to the verse in Isaiah. There it means testimony brought before God. This reading is preferable because the testimony brought before God is what will bring about their calamity.
והאי יתנו עידיהם ויצדקו בעובדי כוכבים כתיב הא בישראל כתיב דאמר ריב"ל כל מצות שישראל עושין בעולם הזה באות ומעידות להם לעוה"ב שנאמר יתנו עידיהם ויצדקו אלו ישראל ישמעו ויאמרו אמת אלו עובדי כוכבים
But does the verse, Let them bring their witnesses that they may be justified, refer to idolaters? It is written about Israel; as R. Joshua b. Levi said: All the commandments which Israel performs in this world will come and testify on their behalf in the world to come, as it is said: Let them bring their witnesses that they may be justified this refers to Israel; And let them hear and say: It is true this refers the idolaters.
The problem is that the verse from Isaiah does not refer to idolaters. The word testimonies/witnesses refers to Israelites.
אלא אמר רב הונא בריה דרב יהושע מאן דאמר עידיהן מהכא (ישעיהו מד, ט) יוצרי פסל כולם תוהו וחמודיהם בל יועילו ועידיהם המה
Rather, R. Huna the son of R. Joshua said that the one who says edehem with an aleph derives it from here: They that fashion a graven image are all nothing, and their delectable things shall not profit, and their own witnesses see not (Isaiah 44:9).
R. Huna son of R. Joshua finds another verse that uses the word edehem with an aleph and clearly refers to idolaters.