Because I Said So: Reading Rabbinic Power

What are the actions for which we bless "asher kidshanu b'mitzvotav?"

מַתְנִי׳ כְּלָל אָמְרוּ בִּיבָמָה: כֹּל שֶׁהִיא אִיסּוּר עֶרְוָה — לֹא חוֹלֶצֶת וְלֹא מִתְיַיבֶּמֶת. אִיסּוּר מִצְוָה וְאִיסּוּר קְדוּשָּׁה — חוֹלֶצֶת וְלֹא מִתְיַיבֶּמֶת.

Yevamot 20a:6

MISHNA: The Sages stated a principle about a yevama: Whoever is forbidden by a prohibition of forbidden relations to her yavam neither performs ḥalitza nor enters into levirate marriage and is completely exempt. If she is forbidden by a prohibition resulting from a mitzva or by a prohibition stemming from sanctity, as will be explained later, then since in these cases the obligation of levirate marriage is not fundamentally nullified she performs ḥalitza in order to become free of the levirate bond, and due to her prohibition she does not enter into levirate marriage.

יבמות כ׳ א:ז׳

אֲחוֹתָהּ שֶׁהִיא יְבִמְתָּהּ — חוֹלֶצֶת אוֹ מִתְיַיבֶּמֶת.

Yevamot 20a:7

The Sages stated another principle: If two sisters who had been married to two brothers who subsequently died happened before the third brother for levirate marriage, and one of those sisters is a close relation to this third brother and is therefore forbidden to him, she is exempt from levirate marriage. But the other, her sister who is her yevama, i.e., her sister-in-law, performs ḥalitza or enters into levirate marriage. In this case, they are not ruled to be two sisters who happened before him simultaneously for levirate marriage, since one of them is prohibited to him as a forbidden relation, and therefore she never actually happened before him at all.

יבמות כ׳ א:ח׳

אִיסּוּר מִצְוָה — שְׁנִיּוֹת מִדִּבְרֵי סוֹפְרִים. אִיסּוּר קְדוּשָּׁה — אַלְמָנָה לְכֹהֵן גָּדוֹל, גְּרוּשָׁה וַחֲלוּצָה לְכֹהֵן הֶדְיוֹט, מַמְזֶרֶת וּנְתִינָה לְיִשְׂרָאֵל, וּבַת יִשְׂרָאֵל לְנָתִין וּמַמְזֵר.

Yevamot 20a:8

The mishna explains: A prohibition resulting from a mitzva is referring to secondary forbidden relationships, which are prohibited by rabbinic law. The Sages prohibited marriage to certain women who were not forbidden by the Torah but were nevertheless deemed forbidden incestuous relations. A prohibition stemming from sanctity is referring to marriage of a widow to a High Priest, a divorcée or a woman who has performed ḥalitza [ḥalutza] to a common priest, a daughter born from an incestuous or adulterous relationship [mamzeret] or a Gibeonite woman to an Israelite, and also an Israelite woman to a Gibeonite or to a son born from an incestuous or adulterous relationship [mamzer].

END OF MISHNAH

יבמות כ׳ א:י״א

אֲחוֹתָהּ שֶׁהִיא יְבִמְתָּהּ. אֲחוֹתָהּ דְּמַאן? אִילֵימָא דְּאִיסּוּר מִצְוָה, כֵּיוָן דְּמִדְּאוֹרָיְיתָא רַמְיָא קַמֵּיהּ, פָּגַע בַּאֲחוֹת זְקוּקָתוֹ! אֶלָּא אֲחוֹתָהּ דְּאִיסּוּר עֶרְוָה.

Yevamot 20a:11

The mishna states: Her sister who is her yevama performs ḥalitza or enters into levirate marriage. The Gemara clarifies this: Whose sister? If we say it is the sister of one who is forbidden due to a prohibition resulting from a mitzva, since by Torah law she is cast before him for levirate marriage, then this would in fact simply be a case of two sisters who fell simultaneously before him, both requiring levirate marriage, since according to Torah law there is no prohibition against entering into levirate marriage with such a woman. If so, it turns out that he encounters the sister of the woman with whom he has a levirate bond; but that case has already been taught. Rather, it must refer to the sister of a woman who is forbidden to him by a prohibition of forbidden relations, and since he may not enter into levirate marriage with a forbidden relation, her sister is not considered to be the sister of a woman with whom he has a levirate bond. Therefore, the sister may be taken in levirate marriage.

1) With what questions are the rabbis wrestling here? What are their concerns?
2) How do they answer their questions? What new idea do they introduce?

יבמות כ׳ א:י״ב

אִיסּוּר מִצְוָה — שְׁנִיּוֹת. אַמַּאי קָרֵי לֵיהּ אִיסּוּר מִצְוָה? אֲמַר אַבָּיֵי: מִצְוָה לִשְׁמוֹעַ דִּבְרֵי חֲכָמִים.

Yevamot 20a:12

The mishna states that a prohibition resulting from a mitzva is referring to secondary forbidden relationships, which are prohibited by rabbinic law. The Gemara asks: Why is this called a prohibition resulting from a mitzva? Abaye said: This is because it is a mitzva to listen to and obey the words of the Sages.

דברים י״ז:ח׳-י״א

(ח) כִּ֣י יִפָּלֵא֩ מִמְּךָ֨ דָבָ֜ר לַמִּשְׁפָּ֗ט בֵּֽין־דָּ֨ם ׀ לְדָ֜ם בֵּֽין־דִּ֣ין לְדִ֗ין וּבֵ֥ין נֶ֙גַע֙ לָנֶ֔גַע דִּבְרֵ֥י רִיבֹ֖ת בִּשְׁעָרֶ֑יךָ וְקַמְתָּ֣ וְעָלִ֔יתָ אֶ֨ל־הַמָּק֔וֹם אֲשֶׁ֥ר יִבְחַ֛ר יְהֹוָ֥ה אֱלֹהֶ֖יךָ בּֽוֹ׃ (ט) וּבָאתָ֗ אֶל־הַכֹּהֲנִים֙ הַלְוִיִּ֔ם וְאֶ֨ל־הַשֹּׁפֵ֔ט אֲשֶׁ֥ר יִהְיֶ֖ה בַּיָּמִ֣ים הָהֵ֑ם וְדָרַשְׁתָּ֙ וְהִגִּ֣ידוּ לְךָ֔ אֵ֖ת דְּבַ֥ר הַמִּשְׁפָּֽט׃ (י) וְעָשִׂ֗יתָ עַל־פִּ֤י הַדָּבָר֙ אֲשֶׁ֣ר יַגִּ֣ידֽוּ לְךָ֔ מִן־הַמָּק֣וֹם הַה֔וּא אֲשֶׁ֖ר יִבְחַ֣ר יְהֹוָ֑ה וְשָׁמַרְתָּ֣ לַעֲשׂ֔וֹת כְּכֹ֖ל אֲשֶׁ֥ר יוֹרֽוּךָ׃ (יא) עַל־פִּ֨י הַתּוֹרָ֜ה אֲשֶׁ֣ר יוֹר֗וּךָ וְעַל־הַמִּשְׁפָּ֛ט אֲשֶׁר־יֹאמְר֥וּ לְךָ֖ תַּעֲשֶׂ֑ה לֹ֣א תָס֗וּר מִן־הַדָּבָ֛ר אֲשֶׁר־יַגִּ֥ידֽוּ לְךָ֖ יָמִ֥ין וּשְׂמֹֽאל׃

Deuteronomy 17:8-11

(8) If a case is too baffling for you to decide, be it a controversy over homicide, civil law, or assault—matters of dispute in your courts—you shall promptly repair to the place that your God יהוה will have chosen, (9) and appear before the levitical priests, or the magistrate in charge at the time, and present your problem. When they have announced to you the verdict in the case, (10) you shall carry out the verdict that is announced to you from that place that יהוה chose, observing scrupulously all their instructions to you. (11) You shall act in accordance with the instructions given you and the ruling handed down to you; you must not deviate from the verdict that they announce to you either to the right or to the left.

רמב"ן על דברים י״ז:י״א:א׳

ימין ושמאל ואל תאמר איך אוכל החלב הגמור הזה או אהרוג האיש הנקי הזה אבל תאמר כך צוה אותי האדון המצוה על המצות שאעשה בכל מצותיו ככל אשר יורוני העומדים לפניו במקום אשר יבחר ועל משמעות דעתם נתן לי התורה אפילו יטעו ... והצורך במצוה הזאת גדול מאד כי התורה נתנה לנו בכתב וידוע הוא שלא ישתוו הדעות בכל הדברים הנולדים והנה ירבו המחלוקות ותעשה התורה כמה תורות וחתך לנו הכתוב הדין שנשמע לבית דין הגדול העומד לפני השם במקום אשר יבחר בכל מה שיאמרו לנו בפירוש התורה בין שקבלו פירושו עד מפי עד ומשה מפי הגבורה או שיאמרו כן לפי משמעות המקרא או כוונתה

Ramban on Deuteronomy 17:11:1

THOU SHALT NOT DEPART FROM THE WORD WHICH THEY SHALL TELL THEE, TO THE RIGHT NOR TO THE LEFT. You are not to say: “How can I [permit myself to] eat this real forbidden fat, or execute this innocent man;” instead you are to say, “The Lord Who enjoined the commandments commanded that I perform all God's commandments in accordance with all that they, who stand before God in the place that God shall choose, teach me to do. God gave me the Torah as taught by them, even if they were to err.” ...
Now the need for this commandment is very great, for the Torah was given to us in written form and it is known that not all opinions concur on newly arising matters. Disagreements would thus increase and the one Torah would become many Torahs. Scripture, therefore, defined the law that we are to obey the Great Court that stands before God in the place that God chose in whatever they tell us with respect to the interpretation of the Torah, whether they received its interpretation by means of witness from witness until Moses [who heard it] from the mouth of the Almighty, or whether they said so based on the implication [of the written words] of the Torah or its intent.

משנה תורה, הלכות ברכות י״א:ג׳

(ג) וְכֵן כָּל הַמִּצְוֹת שֶׁהֵן מִדִּבְרֵי סוֹפְרִים בֵּין מִצְוָה שֶׁהִיא חוֹבָה מִדִּבְרֵיהֶם כְּגוֹן מִקְרָא מְגִלָּה וְהַדְלָקַת נֵר בְּשַׁבָּת וְהַדְלָקַת נֵר חֲנֻכָּה. בֵּין מִצְוֹת שֶׁאֵינָן חוֹבָה כְּגוֹן עֵרוּב וּנְטִילַת יָדַיִם. מְבָרֵךְ עַל הַכּל קדֶם לַעֲשִׂיָּתָן אֲשֶׁר קִדְּשָׁנוּ בְּמִצְוֹתָיו וְצִוָּנוּ לַעֲשׂוֹת. וְהֵיכָן צִוָּנוּ בַּתּוֹרָה. שֶׁכָּתוּב בָּהּ (דברים יז יא) ״אֲשֶׁר יֹאמְרוּ לְךָ תַּעֲשֶׂה״. נִמְצָא עִנְיַן הַדְּבָרִים וְהֶצֵּעָן כָּךְ הוּא. אֲשֶׁר קִדְּשָׁנוּ בְּמִצְוֹתָיו שֶׁצִּוָּה בָּהֶן לִשְׁמֹעַ מֵאֵלּוּ שֶׁצִּוָּנוּ לְהַדְלִיק נֵר שֶׁל חֲנֻכָּה אוֹ לִקְרוֹת אֶת הַמְּגִלָּה. וְכֵן שְׁאָר כָּל הַמִּצְוֹת שֶׁמִּדִּבְרֵי סוֹפְרִים:

Mishneh Torah, Blessings 11:3

(3) So too, all religious duties ordained by the Scribes, whether these are according to their dicta, obligatory; (for example, to read the Scroll of Esther on the Feast of Lots, to kindle lights on the Eve of the Sabbath and during the feast of Chanucah); or whether these duties are optional,—for example, to make an Erub or to wash the hands all require, before they are performed, the recital of a blessing, containing the formula "Who hast sanctified us with Thy commandment and commanded us (to perform that particular duty). Where in the Torah did God so command us? In the text (Deut. 17:11) "… and according to the judgment which they tell thee, thou shalt do." Hence, the meaning and purport of the Benedictory formula is as follows "Who hast sanctified us with Thy commandments among which Thou hast commanded us to give heed to those spiritual leaders who ordained that we should kindle the Chanucah light or read the Scroll of Esther." This applies to all the other duties ordained by the Scribes.