Unlike the Shalosh Regalim, were the Yamim ha-Noraim not part of the original Divine plan? They are initiated by the interaction between the Jewish people and HKBH—specifically, our failure at Chet ha-Egel. This provoked Moshe to intercede on behalf of the nation, with the result that Hashem forgave us. This time of Divine chesed and closeness begins on 1 Elul and culminates on 10 Tishrei, Yom Kippur.

The Timeline of the Year of Yetziyat Mitzrayim, Nisan to Tishrei - Original and Altered

14 Nisan (Thursday, day): The original korban Pesach
15 Nisan (Thursday, night): Makat Bechorot, Yetziyat Mitzrayim (a process which takes approximately a week)
1 Sivan: Bnei Yisrael arrive at Sinai
6 or 7 Sivan (50 days after 15 Nisan): Maamad Har Sinai, Moshe ascends the mountain (an extended discussion of the disclarity about the date is on Shabbat 86b-88a)
7 Sivan to 17 Tammuz: First set of forty days
17 Tammuz: Moshe descends from the mountain with first set of tablets, sees Chet ha-Egel transpiring, breaks first luchot
18 or 19 Tammuz to 29 or 30 Av: Second set of forty days
1 Elul: Moshe makes second set of tablets, ascends the mountain
1 Elul to 10 Tishrei: Third set of forty days
(9 Av of the following year, i.e. the second year after Yetziyat Mitzrayim: Chet ha-Meraglim)
10 Tishrei: Hashem forgives the people, Moshe descends the mountain with second luchot
Moshe's Recounting in Devarim: The First Set of Forty Days
The description of the three sets of forty days is scattered among several parshiyot in Sefer Shemot and retold in Sefer Devarim. The sources below are from Devarim where the description is more compact (all in Parashat Eikev).
Notice that Moshe is not explicit about the timing—that requires an oral tradition!
בַּעֲלֹתִ֣י הָהָ֗רָה לָקַ֜חַת לוּחֹ֤ת הָֽאֲבָנִים֙ לוּחֹ֣ת הַבְּרִ֔ית אֲשֶׁר־כָּרַ֥ת ה׳ עִמָּכֶ֑ם וָאֵשֵׁ֣ב בָּהָ֗ר אַרְבָּעִ֥ים יוֹם֙ וְאַרְבָּעִ֣ים לַ֔יְלָה לֶ֚חֶם לֹ֣א אָכַ֔לְתִּי וּמַ֖יִם לֹ֥א שָׁתִֽיתִי׃
I had ascended the mountain to receive the tablets of stone, the Tablets of the Covenant that ה׳ had made with you, and I stayed on the mountain forty days and forty nights, eating no bread and drinking no water.
Moshe on 17 Tammuz:
וָאֶתְפֹּשׂ֙ בִּשְׁנֵ֣י הַלֻּחֹ֔ת וָֽאַשְׁלִכֵ֔ם מֵעַ֖ל שְׁתֵּ֣י יָדָ֑י וָאֲשַׁבְּרֵ֖ם לְעֵינֵיכֶֽם׃
Thereupon I gripped the two tablets and flung them away with both my hands, smashing them before your eyes.
The Second Set of Forty Days
וָֽאֶתְנַפַּל֩ לִפְנֵ֨י ה׳ כָּרִאשֹׁנָ֗ה אַרְבָּעִ֥ים יוֹם֙ וְאַרְבָּעִ֣ים לַ֔יְלָה לֶ֚חֶם לֹ֣א אָכַ֔לְתִּי וּמַ֖יִם לֹ֣א שָׁתִ֑יתִי עַ֤ל כׇּל־חַטַּאתְכֶם֙ אֲשֶׁ֣ר חֲטָאתֶ֔ם לַעֲשׂ֥וֹת הָרַ֛ע בְּעֵינֵ֥י ה׳ לְהַכְעִיסֽוֹ׃
I threw myself down before ה׳ —eating no bread and drinking no water forty days and forty nights, as before—because of the great wrong you had committed, doing what displeased and vexed ה׳.
The Third Set of Forty Days
בָּעֵ֨ת הַהִ֜וא אָמַ֧ר יְהֹוָ֣ה אֵלַ֗י פְּסׇל־לְךָ֞ שְׁנֵֽי־לוּחֹ֤ת אֲבָנִים֙ כָּרִ֣אשֹׁנִ֔ים וַעֲלֵ֥ה אֵלַ֖י הָהָ֑רָה וְעָשִׂ֥יתָ לְּךָ֖ אֲר֥וֹן עֵֽץ׃
Thereupon יהוה said to me, “Carve out two tablets of stone like the first, and come up to Me on the mountain; and make an ark of wood.
וְאֶכְתֹּב֙ עַל־הַלֻּחֹ֔ת אֶ֨ת־הַדְּבָרִ֔ים אֲשֶׁ֥ר הָי֛וּ עַל־הַלֻּחֹ֥ת הָרִאשֹׁנִ֖ים אֲשֶׁ֣ר שִׁבַּ֑רְתָּ וְשַׂמְתָּ֖ם בָּאָרֽוֹן׃
I will inscribe on the tablets the commandments that were on the first tablets that you smashed, and you shall deposit them in the ark.”
וָאַ֤עַשׂ אֲרוֹן֙ עֲצֵ֣י שִׁטִּ֔ים וָאֶפְסֹ֛ל שְׁנֵי־לֻחֹ֥ת אֲבָנִ֖ים כָּרִאשֹׁנִ֑ים וָאַ֣עַל הָהָ֔רָה וּשְׁנֵ֥י הַלֻּחֹ֖ת בְּיָדִֽי׃
I made an ark of acacia wood and carved out two tablets of stone like the first; I took the two tablets with me and went up the mountain.
The Torah Could Have Been Complete on 17 Tammuz! (Original Timeline)
אָמַר רַבִּי יְהוֹשֻׁעַ בֶּן לֵוִי: מַאי דִּכְתִיב: ״וַיַּרְא הָעָם כִּי בֹשֵׁשׁ מֹשֶׁה״ — אַל תִּקְרֵי ״בּוֹשֵׁשׁ״, אֶלָּא ״בָּאוּ שֵׁשׁ״. בְּשָׁעָה שֶׁעָלָה מֹשֶׁה לַמָּרוֹם אָמַר לָהֶן לְיִשְׂרָאֵל: לְסוֹף אַרְבָּעִים יוֹם בִּתְחִלַּת שֵׁשׁ אֲנִי בָּא. לְסוֹף אַרְבָּעִים יוֹם בָּא שָׂטָן וְעִירְבֵּב אֶת הָעוֹלָם. אָמַר לָהֶן: מֹשֶׁה רַבְּכֶם הֵיכָן הוּא? אָמְרוּ לוֹ: עָלָה לַמָּרוֹם. אָמַר לָהֶן: בָּאוּ שֵׁשׁ, וְלֹא הִשְׁגִּיחוּ עָלָיו. מֵת, וְלֹא הִשְׁגִּיחוּ עָלָיו. הֶרְאָה לָהֶן דְּמוּת מִטָּתוֹ, וְהַיְינוּ דְּקָאָמְרִי לֵיהּ לְאַהֲרֹן: ״כִּי זֶה מֹשֶׁה הָאִישׁ וְגוֹ׳״.
And Rabbi Yehoshua ben Levi said: What is the meaning of that which is written: “And the people saw that Moses delayed [boshesh] to come down from the mount” (Exodus 32:1)? Do not read the word in the verse as boshesh; rather, read it as ba’u shesh, six hours have arrived. When Moses ascended on High, he told the Jewish people: In forty days, at the beginning of six hours, I will come. After forty days, Satan came and brought confusion to the world by means of a storm, and it was impossible to ascertain the time. Satan said to the Jews: Where is your teacher Moses? They said to him: He ascended on High. He said to them: Six hours have arrived and he has not yet come. Surely he won’t. And they paid him no attention. Satan said to them: Moses died. And they paid him no attention. Ultimately, he showed them an image of his death-bed and an image of Moses’ corpse in a cloud. And that is what the Jewish people said to Aaron: “For this Moses, the man who brought us up out of the land of Egypt, we know not what has become of him” (Exodus 32:1).
Instead, an Alternate Timeline is Created
חֲמִשָּׁה דְבָרִים אֵרְעוּ אֶת אֲבוֹתֵינוּ בְּשִׁבְעָה עָשָׂר בְּתַמּוּז וַחֲמִשָּׁה בְּתִשְׁעָה בְאָב. בְּשִׁבְעָה עָשָׂר בְּתַמּוּז נִשְׁתַּבְּרוּ הַלּוּחוֹת, וּבָטַל הַתָּמִיד, וְהֻבְקְעָה הָעִיר, וְשָׂרַף אַפּוֹסְטֹמוֹס אֶת הַתּוֹרָה, וְהֶעֱמִיד צֶלֶם בַּהֵיכָל. בְּתִשְׁעָה בְאָב נִגְזַר עַל אֲבוֹתֵינוּ שֶׁלֹּא יִכָּנְסוּ לָאָרֶץ, וְחָרַב הַבַּיִת בָּרִאשׁוֹנָה וּבַשְּׁנִיָּה, וְנִלְכְּדָה בֵיתָר, וְנֶחְרְשָׁה הָעִיר. מִשֶּׁנִּכְנַס אָב, מְמַעֲטִין בְּשִׂמְחָה:
The mishna discusses the five major communal fast days. Five calamitous matters occurred to our forefathers on the seventeenth of Tammuz, and five other disasters happened on the Ninth of Av. On the seventeenth of Tammuz the tablets were broken by Moses when he saw that the Jews had made the golden calf; the daily offering was nullified by the Roman authorities and was never sacrificed again; the city walls of Jerusalem were breached; the general Apostemos publicly burned a Torah scroll; and Manasseh placed an idol in the Sanctuary. On the Ninth of Av it was decreed upon our ancestors that they would all die in the wilderness and not enter Eretz Yisrael; and the Temple was destroyed the first time, in the days of Nebuchadnezzar, and the second time, by the Romans; and Beitar was captured; and the city of Jerusalem was plowed, as a sign that it would never be rebuilt. Not only does one fast on the Ninth of Av, but from when the month of Av begins, one decreases acts of rejoicing.
שֶׁהֲרֵי בְשִׁבְעָה עָשָׂר בְּתַמּוּז נִשְׁתַּבְּרוּ הַלּוּחוֹת, וּבְי"ח שָׂרַף אֶת הָעֵגֶל וְדָן אֶת הַחוֹטְאִים, וּבְי"ט עָלָה שֶׁנֶּאֱמַר וַיְהִי מִמָּחֳרָת וַיֹּאמֶר מֹשֶׁה אֶל הָעָם וְגוֹ' (שמות ל"ב), וְעָשָׂה שָׁם אַרְבָּעִים יוֹם וּבִקֵּשׁ רַחֲמִים, שֶׁנֶּ' וָאֶתְנַפַּל לִפְנֵי ה׳ וְגוֹ' (דברים ט'), וּבְרֹאשׁ חֹדֶשׁ אֱלוּל נֶאֱמַר לוֹ וְעָלִיתָ בַבֹּקֶר אֶל הַר סִינַי (שמות ל"ד), לְקַבֵּל לוּחוֹת הָאַחֲרוֹנוֹת – וְעָשָׂה שָׁם מ' יוֹם, שֶׁנֶּאֱמַר בָּהֶם וְאָנֹכִי עָמַדְתִּי בָהָר כַּיָּמִים הָרִאשׁוֹנִים וְגוֹ' – מָה הָרִאשׁוֹנִים בְּרָצוֹן אַף הָאַחֲרוֹנִים בְּרָצוֹן, אֱמֹר מֵעַתָּה אֶמְצָעִיִּים הָיוּ בְכַעַס – בְּעֲשָׂרָה בְּתִשְׁרֵי נִתְרַצָּה הַקָּבָּ"ה לְיִשְׂרָאֵל בְּשִׂמְחָה וּבְלֵב שָׁלֵם, וְאָמַר לוֹ לְמֹשֶׁה סָלַחְתִּי, וּמָסַר לוֹ לוּחוֹת אַחֲרוֹנוֹת, וְיָרַד וְהִתְחִיל לְצַוּוֹתָם עַל מְלֶאכֶת הַמִּשְׁכָּן, וַעֲשָׂאוּהוּ עַד אֶחָד בְּנִיסָן, וּמִשֶּׁהוּקַם לֹא נִדְבַּר עִמּוֹ עוֹד אֶלָּא מֵאֹהֶל מוֹעֵד (תנחומא):
For on the seventeenth of Tammuz the tablets were broken, on the eighteenth he burnt the calf and punished the offenders, on the nineteenth he ascended the mountain, as it is said (Exodus 32:30) “And it came to pass on the morrow (the day after he had punished the wrongdoers; cf. vv. 26—29), that Moses said unto the people”, [Ye have sinned a great sin and now I will go up to the Lord]”. There he spent forty days and sought mercy for the people, as it is said, (Deuteronomy 9:18) “And I threw myself down before the Lord [as at the first, forty days and forty nights]”. On the first day of the New Moon of Elul it was said to him, (Exodus 34:2) “And be ready in the morning] and go up in the morning unto mount Sinai” — to receive the second tablets. He again spent there the forty days of which it is stated, (Deuteronomy 10:10) “[And I stayed in the mountain, according to the first, days, [forty days and forty nights]”. How were the first forty days passed? In God’s good-will. So, too, the last forty days were passed in God’s good-will — from which you must admit that the intervening forty days were passed in God’s anger. On the tenth of Tishri God became reconciled with Israel in joy and perfect affection and said to Moses: “I have forgiven!” and handed him over the second tablets, whereupon Moses went down and began to command them concerning the work of the Tabernacle (cf. Midrash Tanchuma, Ki Tisa 31; Seder Olam 6; Rashi on Exodus 18:13, Deuteronomy 9:18 and also Taanit 36b). They were occupied in its construction until the first of Nisan and from the time when it was set up God did not converse with him any more except from the tent of meeting.
כי בשש משה. כְּתַרְגּוּמוֹ, לְשׁוֹן אִחוּר, וְכֵן בֹּשֵׁשׁ רִכְבּוֹ (שופטים ה'), וַיָּחִילוּ עַד בּוֹשׁ (שם ג'); כִּי כְּשֶׁעָלָה מֹשֶׁה לָהָר אָמַר לָהֶם לְסוֹף אַרְבָּעִים יוֹם אֲנִי בָא בְּתוֹךְ שֵׁשׁ שָׁעוֹת, כִּסְבוּרִים הֵם שֶׁאוֹתוֹ יוֹם שֶׁעָלָה מִן הַמִּנְיָן הוּא, וְהוּא אָמַר לָהֶם שְׁלֵמִים – אַרְבָּעִים יוֹם וְלֵילוֹ עִמּוֹ – וְיוֹם עֲלִיָּתוֹ אֵין לֵילוֹ עִמּוֹ, שֶׁהֲרֵי בְז' בְּסִיוָן עָלָה, נִמְצָא יוֹם אַרְבָּעִים בְּשִׁבְעָה עָשָׂר בְּתַמּוּז. בְּי"ו בָּא שָׂטָן וְעִרְבֵּב אֶת הָעוֹלָם, וְהֶרְאָה דְּמוּת חֹשֶׁךְ וַאֲפֵלָה וְעִרְבּוּבְיָה, לוֹמַר וַדַּאי מֵת מֹשֶׁה לְכָךְ בָּא עִרְבּוּבְיָא לָעוֹלָם, אָמַר לָהֶם מֵת מֹשֶׁה, שֶׁכְּבָר בָּאוּ שֵׁשׁ שָׁעוֹת וְלֹא בָּא וְכוּ' כִּדְאִיתָא בְמַסֶּכֶת שַׁבָּת (דף פ"ט); וְאִי אֶפְשָׁר לוֹמַר שֶׁלֹא טָעוּ אֶלָּא בְּיוֹם הַמְעֻנָּן בֵּין קֹדֶם חֲצוֹת בֵּין לְאַחַר חֲצוֹת, שֶׁהֲרֵי לֹא יָרַד מֹשֶׁה עַד יוֹם הַמָּחֳרָת, שֶׁנֶּאֱמַר וַיַּשְׁכִּימוּ מִמָּחֳרָת וַיַּעֲלוּ עֹלֹת:
כי בשש משה [AND WHEN THE PEOPLE SAW] THAT MOSES DELAYED LONG — Understand (בשש as the Targum does, as an expression denoting “lateness”.. Similar are: (Judges 5:28) “[Why is] his chariot so long (בשש) [in coming]?”; (Judges 3:25) “And they waited until it was late (עד בוש)”. For when Moses ascended the mountain he said to them (to the Israelites): at the end of a period of forty days (i. e. on the fortieth day) I shall return during the first six hours of the day (before noon). They thought that the day on which he ascended the mountain (the seventh of Sivan) was to be included in this number (thus — Sivan having 30 days — he was expected back before noon on the sixteenth of Tammuz). In fact, however, he had said to them “after forty days” meaning complete days — forty days, each day together with its night that precedes it — (as is the customary Jewish reckoning; cf. Genesis 1:5: ויהי ערב ויהי בקר). Now, as regards the day of this ascent, its night was not part of it that it can be reckoned as a complete day, for he ascended on the seventh of Sivan early in the morning (cf. Rashi on Exodus 19:3); it follows therefore that the fortieth day really fell on the seventeenth of Tammuz and not as the people had believed on the sixteenth. On the sixteenth of Tammuz Satan came and threw the world into confusion, giving it the appearance of darkness, gloom and disorder that people should say: “Surely Moses is dead, and that is why confusion has come into the world!” He said to them, “Yes, Moses is dead, for six hours (noon) has already come (בשש = ‎בא שש) and he has not returned etc.” — as is related in Treatise Shabbat 89a (cf. Rashi and Tosafot there and Tosafot on Bava Kamma 82a ד"ה כדי). One cannot, however, say that they erred only on account of it being a cloudy day, their mistake consisting in not being able to distinguish between forenoon and afternoon, and that thus they were correct in their supposition that he was to return on the sixteenth of Tammuz; for this assumes that he really returned on the day when they made the calf, but that they were under the impression that noon was past — for, as a matter of fact, Moses did not come down until the following day (the day after they had made the calf), for it is said (v. 6) “And they rose up early in the morrow, and brought up burnt offerings”— and only after wards the Lord said to Moses (v. 7) “Go, go down; for thy people … have corrupted themselves”.
ומשה עלה. בַּיּוֹם הַשֵּׁנִי; וְכָל עֲלִיּוֹתָיו בְּהַשְׁכָּמָה הָיוּ, שֶׁנֶּאֱמַר "וַיַּשְׁכֵּם מֹשֶׁה בַבֹּקֶר" (שמות ל"ד):
ומשה עלה AND MOSES WENT UP on the second day of the month (Mekhilta d'Rabbi Yishmael 19:3); for all his ascents to the mountain were made early in the morning, as it is stated (Exodus 34:4) “And Moses rose up early in the morning [and went up unto mount Sinai]” (Shabbat 86b).

The second set of luchot is given on 10 Tishrei

אָמַר רַבָּן שִׁמְעוֹן בֶּן גַּמְלִיאֵל: לֹא הָיוּ יָמִים טוֹבִים לְיִשְׂרָאֵל כַּחֲמִשָּׁה עָשָׂר בְּאָב וּכְיוֹם הַכִּפּוּרִים. בִּשְׁלָמָא יוֹם הַכִּפּוּרִים — מִשּׁוּם דְּאִית בֵּיהּ סְלִיחָה וּמְחִילָה, יוֹם שֶׁנִּיתְּנוּ בּוֹ לוּחוֹת הָאַחֲרוֹנוֹת.
§ The mishna taught that Rabban Shimon ben Gamliel said: There were no days as happy for the Jewish people as the fifteenth of Av and as Yom Kippur. The Gemara asks: Granted, Yom Kippur is a day of joy because it has the elements of pardon and forgiveness, and moreover, it is the day on which the last pair of tablets were given.
שניתנו בו לוחות אחרונות – שבי"ז בתמוז ירד משה מן ההר תחלה ושיבר את הלוחות ובי"ח טחן את העגל ודן את הפושעים ועלה למרום נשתהה שם שמונים יום ארבעים יום עמד בתפלה דכתיב (דברים ט׳:ט׳) ואתנפל לפני ה׳ ארבעים יום וארבעים לילה וארבעים יום עמד כבראשונה חשוב מי"ז בתמוז עד יום הכפורים והוו להו שמונים יום שנים עשרה שנשתיירו מתמוז דהוא חסר ושלשים דאב ותשעה ועשרים דאלול הרי אחד ושבעים ותשעה דתשרי הרי שמונים יום וליל צום השלים כנגד לילו של י"ז תמוז דלא הוה בחושבניה דהא נפק ליה כבר בשעה שעלה השתא הוי להו פ' שלמין לילה ויום ובוקר יום כפור ירד שהוא עשרה בתשרי ואותו היום נקבע ליום כפור להודיע שמחל וניחם על הרעה אשר דבר לעשות לעמו ועל כן נקבע צום כפור בעשרה בתשרי כך שמעתי:
For on the seventeenth of Tammuz the tablets were broken, on the eighteenth he burnt the calf and punished the offenders, on the nineteenth he ascended the mountain, as it is said (Shemot 32:30) “And it came to pass on the morrow (the day after he had punished the wrongdoers; cf. vv. 26—29), that Moshe said unto the people”, [Ye have sinned a great sin and now I will go up to the Lord]”. There he spent forty days and sought mercy for the people, as it is said, (Devarim 9:18) “And I threw myself down before the Lord [as at the first, forty days and forty nights]”. On the first day of the New Moon of Elul it was said to him, (Shemot 34:2) “And be ready in the morning] and go up in the morning unto mount Sinai” — to receive the second tablets. He again spent there the forty days of which it is stated, (Devarim 10:10) “[And I stayed in the mountain, according to the first, days, [forty days and forty nights]”. How were the first forty days passed? In G-d’s good-will. So, too, the last forty days were passed in G-d’s good-will — from which you must admit that the intervening forty days were passed in G-d’s anger. On the tenth of Tishri G-d became reconciled with Israel in joy and perfect affection and said to Moshe: “I have forgiven!” and handed him over the second tablets, whereupon Moshe went down and began to command them concerning the work of the Tabernacle (cf. Midrash Tanchuma, Ki Tisa 31; Seder Olam 6; Rashi on Shemot 18:13, Devarim 9:18 and also Taanit 36b). They were occupied in its construction until the first of Nisan and from the time when it was set up G-d did not converse with him any more except from the tent of meeting.
Seder Olam's Summary:
ביום השביעי אחר עשרת הדברות עלה משה להר, שנאמר וישכן כבוד ה׳ על הר סיני ויכסהו הענן ששת ימים (שמות כד טז), לטהרו למשה, ויקרא אל משה ביום השביעי מתוך הענן וגו', ויבא משה בתוך הענן ויעל אל ההר ויהי משה בהר ארבעים יום וארבעים לילה (שם), בי"ז בתמוז ירד ושבר את הלוחות, ויהי ממחרת ויאמר משה אל העם אתם חטאתם וגו' (שם לב ל), עלה בשמנה עשר בתמוז, וביקש רחמים על ישראל, דכתיב ואתנפל לפני ה׳ את ארבעים היום ואת ארבעים הלילה אשר התנפלתי כי אמר ה׳ וגו' (דברי ט כה), באותה שעה נתרצה הקב"ה לישראל ואמר למשה לפסול לוחות שניות ולעלות, שנאמר בעת ההוא אמר ה׳ אלי פסל לך שני לוחת אבנים כראשנים ועלה אלי ההרה ועשית לך ארון עץ (שם י א), ירד בעשרים ושמנה באב ופסל שני לוחות, שנאמר ויפסל שני לחת אבנים כראשנים וישכם משה בבקר וגו' (שמות לד ד), ועלה בעשרים ותשעה באב ונשנית לו תורה פעם שניה, שנאמר ואנכי עמדתי בהר כימים הראשנים ארבעים יום וארבעים לילה וגו' לא אבה ה׳ השחיתך (דברים י י), כימים הראשנים, מה הראשונים מרוצין, אף שניים מרוצין, אמור מעתה אמצעיים בכעס, ירד בי' בתשרי והוא היה יום הכיפורים, ובישרם שנתרצה לפני המקום, שנאמר וסלחת לעוננו ולחטאתנו ונחלתנו (שמות לד ט), לפיכך נתקיים יום חוק וזכרון לדורות, שנאמר והיתה זאת לכם לחקת עולם (ויקרא טז לד).
On the seventh day after the Ten Commandments Moshe went up on the mountain, as it says "The Presence of the LORD abode on Mount Sinai, and the cloud hid it for six days..." (Shemot 24:16) This was in order for Moshe to purify himself. "On the seventh day He called to Moses from the midst of the cloud." (ibid.) "Moses went inside the cloud and ascended the mountain; and Moses remained on the mountain forty days and forty nights." (Shemot 24:18) On the 17th of Tammuz he came down and shattered the tablets, "The next day Moses said to the people, 'You have been guilty of a great sin. Yet I will now go up to the LORD; perhaps I may win forgiveness for your sin.'” Moshe went back up on the 18th of Tammuz and pleaded for mercy on behalf of Israel, as it is written "When I lay prostrate before the LORD those forty days and forty nights, because the LORD was determined to destroy you," (Devarim 9:25) At that moment, the Holy One once again viewed Israel with favor and said to Moshe to carve new tablets and to come up the mountain once again, as it says "Thereupon the LORD said to me, “Carve out two tablets of stone like the first, and come up to Me on the mountain; and make an ark of wood." (Devarim 10:1) He came down on the 28th of Av and carved the second tablets, as it says "So Moses carved two tablets of stone, like the first, and early in the morning he went up on Mount Sinai..." (Shemot 34:4) He went back up on the 29th of Av and the Torah was repeated to him a second time, as it says "I had stayed on the mountain, as I did the first time, forty days and forty nights; and the LORD heeded me once again: the LORD agreed not to destroy you." (Devarim 10:10) 'As I did the first time,' just as the first was a time of favor, so too the second were a time of favor- we can derive from this that those in the middle were a time of anger. He came down on the 10th of Tishrei, which was Yom Kippur, and announced to them that they had found favor before God (Hamakom), as it says "Pardon our iniquity and our sin, and take us for Your own!” (Shemot 34:9) Therefore it was established as a fixed day and a remembrance for the generations, as it says "This shall be to you a law for all time: to make atonement for the Israelites for all their sins once a year" (Vayikra 16:34).

So what Torah did we get on Shavuot, and what Torah on Yom Kippur?

הִתְחִיל [משה] מִצְטַעֵר עַל שִׁבּוּר הַלּוּחוֹת, וְאָמַר לוֹ הַקָּדוֹשׁ בָּרוּךְ הוּא אַל תִּצְטָעֵר בַּלּוּחוֹת הָרִאשׁוֹנוֹת, שֶׁלֹא הָיוּ אֶלָּא עֲשֶׂרֶת הַדִּבְּרוֹת לְבָד, וּבַלּוּחוֹת הַשְּׁנִיִּים אֲנִי נוֹתֵן לְךָ שֶׁיְהֵא בָהֶם הֲלָכוֹת מִדְרָשׁ וְאַגָּדוֹת, הֲדָא הוּא דִכְתִיב: וְיַגֶּד לְךָ תַּעֲלֻמוֹת חָכְמָה כִּי כִפְלַיִם לְתוּשִׁיָּה.
...He [Moshe] began to regret that he had broken the tablets, G-d said to him: Do not feel regret about the first tablets, for they only contained the Ten Commandments, however in the second tablets I will give you, that they will contain Halacha, Midrash and Aggadah, as it is written (Job 11): "I will tell you hidden wisdom for it shall be doubly comforting."
וּמָה אֲנִי מְקַיֵּים אֵין בָּאָרוֹן רַק לְרַבּוֹת שִׁבְרֵי לוּחוֹת שֶׁמּוּנָּחִים בָּאָרוֹן וְאִי סָלְקָא דַעְתָּךְ סֵפֶר תּוֹרָה הֶקֵּיפוֹ שִׁשָּׁה טְפָחִים מִכְּדֵי כֹּל שֶׁיֵּשׁ בְּהֶקֵּיפוֹ שְׁלֹשָׁה טְפָחִים יֵשׁ בּוֹ רוֹחַב טֶפַח וְכֵיוָן דִּלְאֶמְצָעִיתוֹ נִגְלָל נְפִישׁ לֵיהּ מִתְּרֵי טִפְחָא רַוְוחָא דְּבֵינֵי בֵּינֵי בִּתְרֵי פּוּשְׁכֵי הֵיכִי יָתֵיב
And accordingly, how do I realize the meaning of that which is stated: “There was nothing in the Ark except the two tablets of stone which Moses put there,” which, according to the opinion of Rabbi Meir, teaches that something else was in the Ark besides the tablets themselves? It serves to include
the broken pieces of the first set of tablets, which were placed in the Ark. Having cited the baraita, the Gemara now presents its objection to what was taught earlier with regard to the dimensions of a Torah scroll: And if it should enter your mind to say, as Rabbi Yehuda HaNasi held, that the circumference of a Torah scroll is six handbreadths, now since any cylindrical object having a circumference of three handbreadths has a diameter of one handbreadth, a Torah scroll with a circumference of six handbreadths has a diameter of two handbreadths. And since a Torah scroll is wound to the middle, since it is rolled from both sides, it must take up more than two handbreadths due to the space between the sheets of parchment and the double rolling. According to Rabbi Meir, who says that the Torah scroll was placed inside the ark, how did the scroll fit in the remaining two handbreadths [pushkei] of space in the Ark?
אָמַר רַבִּי אֶלְעָזָר תּוֹרָה רוֹב בִּכְתָב וּמִיעוּט עַל פֶּה שֶׁנֶּאֱמַר אֶכְתּוֹב לוֹ רוּבֵּי תּוֹרָתִי כְּמוֹ זָר נֶחְשָׁבוּ וְרַבִּי יוֹחָנָן אָמַר רוֹב עַל פֶּה וּמִיעוּט בִּכְתָב שֶׁנֶּאֱמַר כִּי עַל פִּי הַדְּבָרִים הָאֵלֶּה
§ The Gemara continues its discussion concerning the writing of the Torah: Rabbi Elazar says: The majority of the Torah was transmitted in writing, while the minority was transmitted orally, as it is stated: “I wrote for him the greater part of My Torah; they were reckoned a strange thing” (Hosea 8:12), meaning that the majority of the Torah was transmitted in written form. And Rabbi Yoḥanan says: The majority of the Torah was transmitted orally [al peh], while the minority was transmitted in writing, as it is stated with regard to the giving of the Torah to Moses on Mount Sinai: “For on the basis of [al pi] these matters I have made a covenant with you and with Israel” (Exodus 34:27), which indicates that the greater part of the Sinaitic covenant was taught orally.
אָמַר רַבִּי יוֹחָנָן לֹא כָּרַת הַקָּדוֹשׁ בָּרוּךְ הוּא בְּרִית עִם יִשְׂרָאֵל אֶלָּא בִּשְׁבִיל דְּבָרִים שֶׁבְּעַל פֶּה שֶׁנֶּאֱמַר כִּי עַל פִּי הַדְּבָרִים הָאֵלֶּה כָּרַתִּי אִתְּךָ בְּרִית וְאֶת יִשְׂרָאֵל
Rabbi Yoḥanan says: The Holy One, Blessed be He, made a covenant with the Jewish people only for the sake of the matters that were transmitted orally [be’al peh], as it is stated: “For on the basis of [al pi] these matters I have made a covenant with you and with Israel” (Exodus 34:27).
וַיֹּאמֶר ה׳ אֶל מֹשֶׁה כְּתָב לְךָ אֶת הַדְּבָרִים הָאֵלֶּה. זֶה שֶׁאָמַר הַכָּתוּב: אֶכְתָּב לוֹ רֻבֵּי תּוֹרָתִי כְּמוֹ זָר נֶחְשָׁבוּ (הושע ח, יב). אָמַר רַבִּי יְהוּדָה בַּר שַׁלּוּם: כְּשֶׁאָמַר הַקָּדוֹשׁ בָּרוּךְ הוּא לְמֹשֶׁה כְּתָב לְךָ, בִּקֵּשׁ מֹשֶׁה שֶׁתְּהֵא הַמִּשְׁנָה בִּכְתָב. וּלְפִי שֶׁצָּפָה הַקָּדוֹשׁ בָּרוּךְ הוּא שֶׁאֻמּוֹת הָעוֹלָם עֲתִידִין לְתַרְגֵּם אֶת הַתּוֹרָה וְלִהְיוֹת קוֹרְאִין בָּהּ יְוָנִית, וְהֵם אוֹמְרִים אָנוּ יִשְׂרָאֵל.
And the Lord said unto Moses: “Write thou these words, for after the tenor of these words I have made a covenant with thee and with Israel” (Exod. 34:27). Scripture states elsewhere in allusion to this verse: Though I write for him never so many things of My Law, they are accounted as stranger’s (Hos. 8:12). R. Judah the son of Shalum was of the opinion that when the Holy One, blessed be He, said to Moses Write thou, Moses wanted to write the Mishnah as well. However, the Holy One, blessed be He, foresaw that ultimately the nations of the world would translate the Torah into the Greek language and would claim: “We are the Israelites.”
וְעַד עַכְשָׁו הַמֹּאזְנַיִם מְעֻיָּן. אָמַר לָהֶם הַקָּדוֹשׁ בָּרוּךְ הוּא לָאֻמּוֹת: אַתֶּם אוֹמְרִים שֶׁאַתֶּם בָּנַי, אֵינִי יוֹדֵעַ, אֶלָּא מִי שֶׁמִּסְטוֹרִין שֶׁלִּי אֶצְלוֹ, הֵם בָּנַי. וְאֵיזוֹ הִיא? זוֹ הַמִּשְׁנָה שֶׁנִּתְּנָה עַל פֶּה, וְהַכֹּל מִמְּךָ לִדְרֹשׁ.
Now the scales are balanced (as to who are His people). The Holy One, blessed be He, can say to the nations of the world: You claim that you are My children, but I know that only those who know My secrets are My children. Where are His secrets (to be found)? In the Mishnah, which was given orally, and from which everything can be derived.

Could It Have Been Different?

Having seen that תושב"כ and תושבע"פ both present Yom Kippur as a contingent holiday - one that was not in the "original timeline" but rather created in response to actions of Bnei Yisrael - we might want to ask: Do we chart the path of our own progress?
Below is an example of another axial but contingent moment during the journey from Mitzrayim to Eretz Yisrael: the Cheit ha-Meraglim, the sin of the scouts sent to report on conditions in Israel in the second year of the exodus. Note the differences between the account in Bemidbar and Moshe's retelling in Devarim.
(א) וַיְדַבֵּ֥ר ה׳ אֶל־מֹשֶׁ֥ה לֵּאמֹֽר׃ (ב) שְׁלַח־לְךָ֣ אֲנָשִׁ֗ים וְיָתֻ֙רוּ֙ אֶת־אֶ֣רֶץ כְּנַ֔עַן אֲשֶׁר־אֲנִ֥י נֹתֵ֖ן לִבְנֵ֣י יִשְׂרָאֵ֑ל אִ֣ישׁ אֶחָד֩ אִ֨ישׁ אֶחָ֜ד לְמַטֵּ֤ה אֲבֹתָיו֙ תִּשְׁלָ֔חוּ כֹּ֖ל נָשִׂ֥יא בָהֶֽם׃ (ג) וַיִּשְׁלַ֨ח אֹתָ֥ם מֹשֶׁ֛ה מִמִּדְבַּ֥ר פָּארָ֖ן עַל־פִּ֣י ה׳ כֻּלָּ֣ם אֲנָשִׁ֔ים רָאשֵׁ֥י בְנֵֽי־יִשְׂרָאֵ֖ל הֵֽמָּה׃
(1) G-d spoke to Moses, saying, (2) “Send agents to scout the land of Canaan, which I am giving to the Israelite people; send one participant from each of their ancestral tribes, each one a chieftain among them.” (3) So Moses, by G-d’s command, sent them out from the wilderness of Paran, all of them being men of consequence, leaders of the Israelites.
וּבִשְׁלֹ֨חַ ה׳ אֶתְכֶ֗ם מִקָּדֵ֤שׁ בַּרְנֵ֙עַ֙ לֵאמֹ֔ר עֲלוּ֙ וּרְשׁ֣וּ אֶת־הָאָ֔רֶץ אֲשֶׁ֥ר נָתַ֖תִּי לָכֶ֑ם וַתַּמְר֗וּ אֶת־פִּ֤י ה׳ אֱלֹ֣קֵיכֶ֔ם וְלֹ֤א הֶֽאֱמַנְתֶּם֙ ל֔וֹ וְלֹ֥א שְׁמַעְתֶּ֖ם בְּקֹלֽוֹ׃
And when ה׳ sent you on from Kadesh-barnea, saying, “Go up and take possession of the land that I am giving you,” you flouted the command of your God ה׳ —whom you did not put your trust in nor obey.
Rav Y. D. Soloveitchik, Derash on Behaalotcha, June 10, 1974, transcribed by R. Yitzchak Etshalom
Moshe was certain – there was not even a shadow of doubt in his mind – that he was going to enter the promised land. He and the entire congregation will be classified as both Yotz’ei Mitzrayim (departers from Egypt) and Ba’ei ha’Aretz (those who come into the Land). He was sure , he was convinced that he would see the beautiful land, the hills of Judea, the prairie land of the Sharon Valley, he was certain that he will climb the mount of Levanon...The whole operation, if successfully brought to a close would have lasted several days. And at that time there was no need for Meraglim, for scouts to explore the land... The great tragedy happened, the great triumphal final march suddenly came to a stop, the people who rejected the basic principle of economic limitedness and aesthetic enjoyment, these people were not worthy to enter the Land.

The Beit ha-Levi's Tradition

According to the Beit ha-Levi, based on Chazal, the entirety of the תושבע"פ was originally written on the Luchot ha-Brit. At Cheit ha-Egel, it was removed.
...חזר לאחוריו וראוהו הזקנים ורצו אחריו אחז משה בראשי הלוחות והן אחזו בראשן וחזק כחו של משה יותר מכחן של שבעים זקנים שנאמר "ולכל היד החזקה" נסתכל משה בלוחות וראה הכתב שבהן שפורח וכבדו על ידי משה ונפלו מידיו ונשתברו. אחרים אמרו לא שבר עד שנאמר לו מפי הגבורה "אשר שברת" אמר לו יפה כחך ששברת. רבי מאיר אומר "ויהיו שם כאשר צוני" שנצטוה ושבר הלוחות.
...He [Moshe] turned around the elders saw him. They ran after him: Moshe grasped the tops of the tablets and they grasped at them too. But Moshe's strength overcame that of the seventy elders, as it is written, "For all the great might (ha-yad ha-chazakah)"(Devarim 34:12). Moshe looked at the tablets and saw that the writing on them was drifting away. The tablets grew heavy in Moshe's hands [because they now didn't have so many letters etched into them], fell from his hands, and shattered. Others say that only after it was said to him from the mouth of G-d, "which you have broken" (Devarim 34:1). meaning that G-d was communicating to Moshe, "It's a good thing that you broke them." Rabbi Meir adds [that this is also the meaning of the verse], "They [the first, broken tablets] are there [in the ark] as I was commanded" (Devarim 10:5) - only after he was commanded did he break the tablets.
אם בחקותי תלכו דא תורה שבע"פ ואת משפטי תשמרו דא תורה שבכתב. והנה במדרש רבה פרשה כי תשא איתא דנסתכל משה בלוחות וראה שפרח מהם הכתב ועמד ושיברן, וכבר הסברנו הדברים לקמן פרשה כי תשא דבלוחות הראשונים היה כתוב בהם גם התורה שבע"פ...
וע"ד שכתבנו דבזה היה מעלתו משה רבינו שאצלו היה רק שבע"פ... ואמרו בגמרא אין הגליות מתכנסות אלא בזכות המשנה שנאמר "גם כי יתנו בגוים עתה אקבצם", הרי דקיבוץ גליות יהיה בזכות תורה שבע"פ וכמש"כ:
"If you shall walk in my statutes," this is the Oral Torah; "and keep my laws," this is the Written Torah. So we see it brought in Midrash [Shemot] Rabbah, Parashat Ki Tisa that Moshe looked at the tablets and saw that the writing on them was drifting away and then broke them where he stood, and as we explained earlier in Parashat Ki Tisa, on the first set of tablets the Oral Torah was also written...
Another matter: We also wrote that the level attained by Moshe Rabbeinu was only in the Oral Torah... In the Gemara it is say that the diaspora will be gathered only due to the merit of the Mishnah, as it is said, "Even if they are scattered among the nations I will presently gather them together" (Hoshea 8:10) and this kibbutz galuyot will occur due to the merit of the the Oral Torah.
* This idea is also explored in detail in דרשות בית הלוי ס׳ יח (p. 192 in the linked edition; the derashot seems to be numbered differently in some editions and/or printed with the Beit ha-Levi on the Torah).

Rabbi Tzadok ha-Levi of Lublin

In contrast, Rav Tzadok contends the opposite: that the original tablets did not contain the Oral Torah, but rather that the giving of the Oral Law was a tikkun (correction) for sin, a concession to a lesser world.
כמו שמובא בזוה"ק פרשה זו (קס"ו: קס"ז א) ואלמלא חטאו ישראל לא ניתן להם אלא חמישה חומשי תורה וכו' (נדרים כ"ב ב) ואחר הקלקול ניתנו לוחות שניים ביום הכפורים שיש בהם מדרש הלכות ואגדות כפלים לתושיה (שמות רבה מ"ו, א' ומ"ז, ז') שהוא הרוב חכמה לתקן הרוב כעס...
As it is brought down in the holy Zohar on this parashah, had Yisrael not sinned, only the five books of Torah would have been given to them (Nedarim 22b). After the damage [of the sin] the second set of tablets was given on Yom Kippur, which had on them much more Midrash, halachot, and aggadot for their redemption (Shemot Rabbah 46:1, 47:7). These are the greater part of wisdom to act as a corrective to the great anger [of Hashem].
רק יהיה אחר הקלקול יום הכפורים ואז יתן להם לוחות שניים שכלול בהם תורה שבעל פה שמזה בא חילוק מדריגות (כמו שנת' מא' א) ואף שהבחירה נתונה כבר כתב הרמב"ם ז"ל (סו"פ ה מה׳ תשובה) שעל זה נאמר כי לא מחשבותי מחשותיכם וגו' והראב"ד ז"ל כ' עליו שטוב היה לו להניח הדבר בתמימות התמימים וכו' ... וכן כאן צפה השי"ת הקלקול והתיקון ביום הכפורים ושיהיה לוחות שניים...
Only after the damage [of the sin of the golden calf] did Yom Kippur come into being. Then, He gave them the second set of tablets, which included the Oral Torah, the cause of the distinction between the [spiritual] levels [of the people before and after the sin]. Rambam already clarified [in Hilchot Teshuvah] that people possess free will, [a mystery] about which it is said "For My plans are not like your plans" (Yeshayahu 55:8), but the Raavad responded to him that it would be better for him to leave the matter in the manner of the simple... Thus, at this point Hashem foresaw the damage [of the sin] as well as the correction on Yom Kippur, i.e. that there will be two sets of tablets.
(ה) ...כי אע"פ שאמרו נעשה ונשמע הוצרכו ג"כ לכפיית הר כגיגית. ואמרו בתנחומא (שם) שהוא על התושבע"פ שאין לומד אותה אלא מי שאוהב הקב"ה בכל לבו כו' זה תלמוד שצריך שינון כו' יעוש"ב...
ודור באי הארץ אלמלי זכו להיות יגיעים ועמלים בתורה היתה אז ההתגלות דתושבע"פ לגמרי שהיו משיגים כל מה שאפשר להשיג בעוה"ז ולא היו צריכים לגלות כלל. אבל הם פנו כ"א לזיתו ולכרמו ואף בזקנים שאחריו כמשז"ל. לפי שקבלת תושבע"פ שלהם הי' רק בכפייה והכרח ולא מאהבה ושלא מאהבה א"א לייגע בה ולהשיג כלל...
כי יהי אור אז"ל זו תורה דכתיב תורה אור ונא' אח"כ וירא וגו' כי טוב... ואור א' הוא תושב"כ שהוא במאמר ה׳. וכי טוב הוא השגת התושבע"פ הנמשך מהאור דתושב"כ... ולוחות ראשונות הוא האור דתושב"כ...
Even though they said, "We will do and we will hear" (), they required the overturning of the mountain [Har Sinai] like a tub over their heads. As it says in [Midrash] Tanchuma, this [overturning] was about the Oral Torah, since only "one who loves HKBH with all their heart" learns it: this refers to the Talmud, which can only be learned with great effort...
The generation that entered the Land of Israel, had they not had the merit to work hard at learning Torah, there would not have been such an extensive growth of Oral Tradition. Otherwise, they would have attained all that is possible in this world without the need to discover anything. They would have just tended to their olive groves and vineyards and so the following generations. [But the generation of the wilderness], their receipt of the Oral Torah was by coercion and obligation and not from love, and without love it is impossible to attain anything...
"And then there was light," this it the Torah, as it is said of it, "Torah is light," and later it says, "And He saw...that it was good." The first kind of light [of creation] is the Written Torah which is revealed through the speech of G-d. "That it was good" is the attainment of the Oral Torah which is drawn from the light of the Written Torah... The first set of tablets is like the light of the Written Torah...

Is Chanukah the Holiday of the Oral Law? Rav Hutner's Suggestion

But wait...what if Yom Kippur is not the (only) holiday associated with the Oral Torah? Rav Hutner suggests that Chanukah's unwrittenness points to its connection with the Oral Torah. Putting the two ideas together, perhaps we can say that Yom Kippur is about the need for the Oral Tradition whereas Chanukah is about the nature of the transmission of the Oral Tradition.
Rav Yitzhak Hutner, Pachad Yitzhak on Chanukah, Essay 1 [source]
We now that there are some parts of Torah that were meant to be written down, and others that were specifically not intended to be written down. This idea extents beyond the Torah itself. The Gemara in Yoma 29 compares Esther to the daybreak: just as the daybreak is the end of the night, so too was Esther the end of the miracles performed by Hashem for his people (at least open, chronicled miracles). The Gemara then asks what about Chanukah, which came several hundred years later. The Gemara answers that Chanukah does not count, since the Gemara is only speaking of those that were supposed to be written down... The Torah that relates to the miracle of Chanukah was not meant to be written down, since the chronicles of this miracle did not make it into the canon...
Even now that the Oral Torah has been written down, its essence has not disappeared. The Mishna is not always written in the most concise fashion, and the Gemara often explains Mishna by stating that a line is missing or that there is no order to the Mishna or some similar explanation. The point of this is that even once the Oral Torah has been written down, it still needs to rely on the Oral Tradition to help explain it...
We now return to our starting point, namely that the miracle of Chanukah was not meant to be written down...the not-writtenness of the miracle effects its unique nature. Even in the Gemara, there is no tractate about Chanukah, but rather a few pages that come up as a digression of another topic.

The Seder ha-Avodah

The avodah of Yom Kippur cannot be performed without the instruction of the Oral Tradition, which is understood to be expressed by the Kohen Gadol's declaration, "More than what I have read before you is written here."
(א) בָּא לוֹ כֹהֵן גָּדוֹל לִקְרוֹת... וְקוֹרֵא אַחֲרֵי מוֹת וְאַךְ בֶּעָשׂוֹר. וְגוֹלֵל סֵפֶר תּוֹרָה וּמַנִּיחוֹ בְחֵיקוֹ, וְאוֹמֵר, יוֹתֵר מִמַּה שֶּׁקָּרָאתִי לִפְנֵיכֶם כָּתוּב כָּאן
(1) The High Priest came to read the Torah...And he reads from the scroll the Torah portion beginning with the verse: “After the death” (Leviticus 16:1) and the portion beginning with the verse: “But on the tenth” (Leviticus 23:26), and furls the Torah scroll and places it on his bosom and says: More than what I have read before you is written here.
Abudarham, Commentary on Seder ha-Avodah (in Tashlum Abudarham, Berlin 1900)
In his commentary on the Yom Kippur Machzor, Abudarham (14th cen. Spain) records a tradition attributing the composition of the Seder Avodah poem Ata Konanta to an actual kohen gadol, i.e. one who had witnessed himself the ritual in the Beit ha-Mikdash. Though there are dozens of such poems known to us today (and probably many more that have not survived), Atta Konanta is likely the most ancient and was more widely used across the Jewish world before the adoption of medieval piyyutim in its place, as in Ashkenaz.
As Rashi explained (on Yoma 36b), they were then accustomed to create a [poetic] Seder ha-Avodah on Yom Kippur so that it will be considered a remembrance of the act itself, "Instead of bulls we will pay [the offering of] our lips" (Hoshea 14:3). In our liturgies it is recorded that Yose ben Yose the kohen gadol composed Ata Konanata and it is possible that he was among the high priests who served in the second Beit ha-Mikdash or in their company. There are those who say that he was not actually a kohen gadol but rather he was a kohen and great in his generation, and for this reason he is referred to as a kohen gadol. In any case he was one of the classical liturgical poets, as wrote R. Aharon ha-Kohen...

Joy, Teshuvah, Renewal, Joy Again

As Rav Lichtenstein summarizes, Shavuot and Yom Kippur are intrinsically linked, sharing themes of revelation and renewal. While we are accustomed to thinking of Shavuot as a joyful holiday and Yom Kippur as a solemn one, how might our perspective change if we remember that Shavuot is connected with teshuvah and Yom Kippur with revelation?
Rav Aharon Lichtenstein, Jewish Action, Fall 2013
The spiritual tension that is central to the process of teshuvah may seem to stand in marked contrast to the aura of Shavuot, and, presumably, better befitting the character of another central date, that of Yom Kippur... There is much which they share in common regarding both their respective historical origins... Each constituted a critical occasion on its own, and yet is also defined, lesha’ah and ledorot, as the conclusion of a process. Each, originally, was marked by epiphanous revelation, and yet, at the same time, the conclusion of each chag is associated with a similar result—namely, the transmission of the Divine Torah to the realm of human experience: Shavuot, familiar as zeman matan Torateinu, the giving of the Torah Shebichtav, and Yom Kippur, although not designated in tefillah as zeman matan Torateinu, is the occasion of the transmission of Torah Shebe’al Peh as a corpus to Moshe Rabbeinu.