The Rebbe on Pirkei Avot 1:1 Five Levels of Personal Mesorah and Compassionate Judgement

(א) משֶׁה קִבֵּל תּוֹרָה מִסִּינַי, וּמְסָרָהּ לִיהוֹשֻׁעַ, וִיהוֹשֻׁעַ לִזְקֵנִים, וּזְקֵנִים לִנְבִיאִים, וּנְבִיאִים מְסָרוּהָ לְאַנְשֵׁי כְנֶסֶת הַגְּדוֹלָה. הֵם אָמְרוּ שְׁלשָׁה דְבָרִים, הֱווּ מְתוּנִים בַּדִּין, וְהַעֲמִידוּ תַלְמִידִים הַרְבֵּה, וַעֲשׂוּ סְיָג לַתּוֹרָה:

(1) Moshe received the Torah from Sinai and transmitted it to Yehoshua, and Yehoshua to the Elders, and the Elders to the Prophets, and the Prophets transmitted it to the Men of the Great Assembly.

They said three things: Be deliberate in judgment, raise up many disciples and make a fence for the Torah.

Preliminary Questions:
1. What's the connection between the two parts of the Mishna? They seem unrelated, so why not just separate them?

2. Why list all the levels of the Mesorah? Couldn't it have said that Moshe received from Hashem and passed it on through the generations until the Men of the Great Assembly?

3. There were many other steps of the Mesorah that are not included in this list. Why specifically these five?
4. A prophet cannot use his gift of prophecy to pass a Torah law. Why are prophets included in the Mesorah of the oral tradition?
5. If Moshe is the greatest prophet of all time, why not call him a prophet here since they have included prophets in the oral tradition?

מה' טובא הוו כדתניא הרבה נביאים עמדו להם לישראל כפלים כיוצאי מצרים אלא נבואה שהוצרכה לדורות נכתבה ושלא הוצרכה לא נכתבה

However, only a portion of the prophecies were recorded, because only prophecy that was needed for future generations was written down in the Bible for posterity, but that which was not needed, as it was not pertinent to later generations, was not written.

תּוֹרָ֥ה צִוָּה־לָ֖נוּ מֹשֶׁ֑ה מוֹרָשָׁ֖ה קְהִלַּ֥ת יַעֲקֹֽב׃

When Moses charged us with the Teaching As the heritage of the congregation of Jacob.

Moshe represents the humility - the Bitul of Chochma, a complete giving over of oneself to the divinity of Torah - that is required to launch a lifetime of study.
וְדִבֶּר ה' אֶל־מֹשֶׁה פָּנִים אֶל־פָּנִים כַּאֲשֶׁר יְדַבֵּר אִישׁ אֶל־רֵעֵהוּ וְשָׁב אֶל־הַמַּחֲנֶה וּמְשָׁרְתוֹ יְהוֹשֻׁעַ בִּן־נוּן נַעַר לֹא יָמִישׁ מִתּוֹךְ הָאֹהֶל׃

The LORD would speak to Moses face to face, as one man speaks to another. And he would then return to the camp; but his attendant, Joshua son of Nun, a youth, would not stir out of the Tent.

נֹצֵ֣ר תְּ֭אֵנָה יֹאכַ֣ל פִּרְיָ֑הּ וְשֹׁמֵ֖ר אֲדֹנָ֣יו יְכֻבָּֽד׃

He who tends a fig tree will enjoy its fruit, And he who cares for his master will be honored.

Yehoshua represents the devotion, dedication and Kabbalat Ol that is the next step in acquiring Torah. After accepting that the Torah is G-d's wisdom with complete humility, a person dedicating him or herself to Torah knows they must put in the time and effort and "not leave the tent." This stage is still very much in the process of receiving.

רבי יוסי הגלילי אומר אין זקן אלא מי שקנה חכמה שנאמר ה׳ קנני ראשית דרכו

Rabbi Yosei HaGelili says: An “elder [zaken]” means nothing other than one who has acquired wisdom. He interprets the word zaken as a contraction of the phrase zeh kanna, meaning: This one has acquired. Elsewhere the word kanna is used in reference to wisdom, as it is stated that wisdom says: “The Lord acquired me [kanani] at the beginning of His way” (Proverbs 8:22).

The Mesorah passes to the Zekanim, who enjoy and delight in understanding the wisdom of the Torah they have received.
ואמר רב יהודה אמר רב כל הפסוק הזה לא אמרו דואג אלא בלשון הרע יודע נגן שיודע לישאל גבור שיודע להשיב איש מלחמה שיודע לישא וליתן במלחמתה של תורה (איש תואר שמראה פנים בהלכה ונבון דבר שמבין דבר מתוך דבר) וה' עמו שהלכה כמותו בכל מקום

Rav Yehuda says that Rav says: Doeg the Edomite, one of Saul’s servants, stated this entire verse only as malicious speech, in an attempt to incite Saul to be jealous of David. “Who knows how to play” means that he knows how to ask complex and germane questions about Torah matters... “And the Lord is with him” means that the halakha is ruled in accordance with his opinion in every area of halakha.

עמד רבי יהושע על רגליו ואמר (דברים ל, יב) לא בשמים היא מאי לא בשמים היא אמר רבי ירמיה שכבר נתנה תורה מהר סיני אין אנו משגיחין בבת קול שכבר כתבת בהר סיני בתורה (שמות כג, ב) אחרי רבים להטות

Rabbi Yehoshua stood on his feet and said: It is written: “It is not in heaven” (Deuteronomy 30:12). The Gemara asks: What is the relevance of the phrase “It is not in heaven” in this context? Rabbi Yirmeya says: Since the Torah was already given at Mount Sinai, we do not regard a Divine Voice, as You already wrote at Mount Sinai, in the Torah: “After a majority to incline” (Exodus 23:2). Since the majority of Rabbis disagreed with Rabbi Eliezer’s opinion, the halakha is not ruled in accordance with his opinion.

Elders passed it to the Prophets: Our Talmudic sages saw the Halacha as it was in heaven through their power of Ruach Hakodesh, then applied their own understanding to it and made it their own (לא בשמים היא​​​​​​​). Today, we need to ensure that our halachic understanding and rulings are infused with Yirat Shamayim and a desire not to allow our fellow Jews to G-d forbid, do the wrong thing based on our rulings.
והא דרב מתנא מטייא לדרבי יהושע בן לוי דאמר רבי יהושע בן לוי למה נקרא שמן אנשי כנסת הגדולה שהחזירו עטרה ליושנה אתא משה אמר (דברים י, יז) האל הגדול הגבור והנורא אתא ירמיה ואמר נכרים מקרקרין בהיכלו איה נוראותיו לא אמר נורא אתא דניאל אמר נכרים משתעבדים בבניו איה גבורותיו לא אמר גבור אתו אינהו ואמרו אדרבה זו היא גבורת גבורתו שכובש את יצרו שנותן ארך אפים לרשעים ואלו הן נוראותיו שאלמלא מוראו של הקב"ה היאך אומה אחת יכולה להתקיים בין האומות
The Gemara comments: This interpretation that Rav Mattana said leans to, i.e., is consonant with, the exposition of RabbiYehoshua ben Levi. As Rabbi Yehoshua ben Levi said: Why are the Sages of those generations called the members of the Great Assembly? It is because they returned the crown of the Holy One, Blessed be He, to its former glory. How so? Moses came and said in his prayer: “The great, the mighty, and the awesomeGod” (Deuteronomy 10:17). Jeremiah the prophet came and said: Gentiles, i.e., the minions of Nebuchadnezzar, are carousing in His sanctuary; where is His awesomeness? Therefore, he did not say awesome in his prayer: “The great God, the mighty Lord of Hosts, is His name” (Jeremiah 32:18). Daniel came and said: Gentiles are enslaving His children; where is His might? Therefore he did not say mighty in his prayer: “The great and awesome God” (Daniel 9:4). The members of the Great Assembly came and said: On the contrary, this is the might of His might, i.e., this is the fullest expression of it, that He conquers His inclination in that He exercises patience toward the wicked. God’s anger is flared by the gentile nations’ enslavement of His people, yet He expresses tremendous might by suppressing His anger and holding back from punishing them immediately. Therefore, it is still appropriate to refer to God as mighty. And these acts also express His awesomeness: Were it not for the awesomeness of the Holy One, Blessed be He, how could one people, i.e., the Jewish people, who are alone and hated by the gentile nations, survive among the nations?

אין לו להקב"ה בעולמו אלא ארבע אמות של הלכה

Brachot, 8b

There is not for G-d in his world except for the Four Amot of Halacha

The Men of the Great Assembly were able to find the greatness of G-d despite the dark situation they beheld. So too, Torah can transcend even those who misrepresent Torah or hold a generation captive from Torah study. In our lives, it represents the power of Jewish law to impact the physical world in profound ways, shedding light where people have deliberately obscured it to subvert the Torah. Through the study of Halacha and its real-world application, we can uplift the physical and make this world holy and a place where G-d can dwell.
And this is why the second part of the Mishna makes sense that it follows the chain of transmission listed in the first part:

We need to follow the path of the Men of the Great Assembly by interacting within the public domain of the material world. We need to take the רשות הרבים and transform it into a place where the אחדות of 'ה is felt and made visible. When we do this, we will gather many students - הרבה - who study G-d's wisdom and stand them upright so they can continue from one generation to the next, in an eternal chain of tradition.

Whatever G-d asks of the Jewish people to do, G-d does it in some form Himself.
The Rebbe describes how G-d himself conducts Himself in the ways that the sages instruct us to in the first Mishna.

הֱווּ מְתוּנִים בַּדִּין

Hashem is compassionate in His Judgement of the Jewish people, knowing the particular temptations of the current exile we are in.

Chassidic mentor, Rabbi Shmuel Betzalel: "G-d takes the soul - a part of His supernal wisdom - and enclothes it in a package of meat, bones and boiling blood".

וְהַעֲמִידוּ תַלְמִידִים הַרְבֵּה -

Hashem desires that all his children, even those who have strayed - should be able to study Torah. Not just those who have been included in the doors of the study hall, but even the wickedest ones amongst the Jewish people; they too should become children who are learning G-d's ways.

וַעֲשׂוּ סְיָג לַתּוֹרָה:

Through the multiple ways in which Torah is elucidated, there are many ways for those who are first becoming familiar with Judaism can connect to Torah. The various fences that protect Jewish law also act as access points and welcoming gates for everyone to find an entry and a way into Torah study, and then continue their exploration within Torah, having found their place of connection.

רַבִּי חֲנַנְיָא בֶּן עֲקַשְׁיָא אוֹמֵר, רָצָה הַקָּדוֹשׁ בָּרוּךְ הוּא לְזַכּוֹת אֶת יִשְׂרָאֵל, לְפִיכָךְ הִרְבָּה לָהֶם תּוֹרָה וּמִצְוֹת, שֶׁנֶּאֱמַר (ישעיה מב) ה' חָפֵץ לְמַעַן צִדְקוֹ יַגְדִּיל תּוֹרָה וְיַאְדִּיר:

(Makkot 3:16) Rabbi Chananya ben Akashia says, The Holy One, Blessed be He, wanted to give Israel merit; therefore He multiplied for them Torah and commandments, as it said, "The Lord desired, for the sake of His righteousness, to make the Torah great and glorious," (Isaiah 42:21).

The order of this Mishna - Judge with forbearance, assemble large numbers of students and create a fence for the Torah - can be reversed as we enter the Messianic age: We create a fence for the Torah, then assemble many students and then judge with forbearance.
When every Jew has a connection to Torah through its fences, it will lead to every Jew becoming a student of Hashem's ways, which will then lead to the Messianic era. Because of the learning of Torah and acceptance of Mitzvot, Moshiach will not be ushered in through negative judgment but will be a "Triumph through Stillness and Quiet" (Isaiah 30:15)