The Meaning of Communal Mourning

(ו) חמשה דברים ארעו את אבותינו...בתשעה באב: נגזר על אבותינו שלא יכנסו לארץ, וחרב הבית בראשונה ובשניה, ונלכדה ביתר, ונחרשה העיר. משנכנס אב ממעטין בשמחה.

(6) Five events befell our ancestors...On the Ninth of Av: it was decreed upon our ancestors that they would not be allowed to enter the Land of Israel, the First and Second temples were destroyed, Beitar was captured, The city of Jerusalem was plowed over. From when the month of Av starts, we reduce joy.

דברים האסורים בתשעה באב ובו כ"ה סעיפים:
תשעה באב אסור ברחיצה וסיכה ונעילת הסנדל ותשמיש המיטה ואסור לקרות בתורה נביאים וכתובים ולשנות במשנה ובמדרש ובגמ' בהלכות ובאגדות משום שנאמר פקודי ה' ישרים משמחי לב ותינוקות של בית רבן בטלים בו אבל קורא הוא באיוב ובדברים הרעים שבירמיה ואם יש ביניהם פסוקי נחמה צריך לדלגם:

On Tisha b'Av these are forbidden: washing, anointing, wearing leather shoes, and marital relations. It is also forbidden to read from the Torah, Nevi'im, and Ktuvim and to learn Mishna and Midrash and Gemara and Halacha and Aggada, because it says, "The precepts of God are right, gladdening the heart" (Tehillim 19:9). Schoolchildren are idle on this day. But, one may read Job and the harsh parts of Jeremiah, but if these contain passages of consolation, one must skip them.

Rabbi Kenneth Brander, "Where are You?" The Most Important Question of Tisha b'Av
The reason for this opposite pattern is because unlike mourning a family member, it is so hard to sincerely mourn a 2000-year-old tragedy. It’s true that the loss of our holy Temple led to the loss of our sovereignty and, even more significantly, the loss of our connection to God. But still it’s hard to immediately and emotionally connect to it. We need time to enter into the necessary mindset.

אמר רב אשי שאני אבילות חדשה מאבילות ישנה ושאני אבילות דרבים מאבילות דיחיד:

Rav Ashi stated: New mourning is different from old mourning, and the mourning of the public is different from the private mourning of the individual.

Rabbi Joseph B. Soloveitchik, Excerpts from Avelut Yeshanah and Avelut Hadashah: Historical and Individual Mourning
The Gemara (Yevamot 43b) distinguishes between avelut hadashah and avelut yeshanah, "new" mourning and "old," historical mourning - or, expressing the same thought in a different idiom, between avelut de-yahid and avelut de-rabbim, private and national-communal mourning. The first, avelut hadashah, is caused by a death or disaster which strikes a family or an individual. It is a primordial, instinctual, spontaneous response of man to evil, to the traumatic confrontation with death, to the impact of catastrophe and disaster. It is an existential response, not one that evolves by the application of artificial stimuli.
The second category, avelut yeshanah, is due to a historic disaster that took place 1,900 years ago. This category is the handiwork of man. There is no spontaneous reaction to some new event which has just transpired, for nothing new has happened which should justify grief. The avelut is a result of recollection of events. Judaism here introduced a strange kind of memory, a very unique and singular memory.
Even though the mourning of an individual constitutes a kiyyum she-ba-lev, an inner, experiential fulfillment of the obligation to mourn, it must be translated into deeds, into technical observance….The Halakhah demanded that feeling be transposed into deed…that fleeting, amorphous moods be crystallized into real tangible symbols….Avelut yeshanah [mourning a past occurrence] does not establish itself at one bang; the process is generally slow. It…not only notes and gives heed to bygone days but also reexperiences, relives, restages and redramatizes remote events which seem to have forfeited their relevance long ago. The Halakhah could not decree observance of mourning at once. The reawakening takes time; it transpires gradually. It would be absurd, therefore, to start out with the practical observance of mourning before the experience has been reproduced and relived in all its tragic, frightening magnitude. The time between the Seventeenth of Tammuz and Rosh Hodesh Av is exclusively devoted to remembrance, to meditation, to reliving and reexperiencing. Only on Rosh Hodesh Av does the avelut she-ba-lev begin to be recorded on the register of objective mourning and the first signs of observance become visible.

תָּנוּ רַבָּנַן כְּשֶׁחָרַב הַבַּיִת בַּשְּׁנִיָּה רַבּוּ פְּרוּשִׁין בְּיִשְׂרָאֵל שֶׁלֹּא לֶאֱכוֹל בָּשָׂר וְשֶׁלֹּא לִשְׁתּוֹת יַיִן נִטְפַּל לָהֶן רַבִּי יְהוֹשֻׁעַ אָמַר לָהֶן בָּנַי מִפְּנֵי מָה אִי אַתֶּם אוֹכְלִין בָּשָׂר וְאֵין אַתֶּם שׁוֹתִין יַיִן אָמְרוּ לוֹ נֹאכַל בָּשָׂר שֶׁמִּמֶּנּוּ מַקְרִיבִין עַל גַּבֵּי מִזְבֵּחַ וְעַכְשָׁיו בָּטֵל נִשְׁתֶּה יַיִן שֶׁמְּנַסְּכִין עַל גַּבֵּי הַמִּזְבֵּחַ וְעַכְשָׁיו בָּטֵל אָמַר לָהֶם אִם כֵּן לֶחֶם לֹא נֹאכַל שֶׁכְּבָר בָּטְלוּ מְנָחוֹת אֶפְשָׁר בְּפֵירוֹת פֵּירוֹת לֹא נֹאכַל שֶׁכְּבָר בָּטְלוּ בִּכּוּרִים אֶפְשָׁר בְּפֵירוֹת אֲחֵרִים מַיִם לֹא נִשְׁתֶּה שֶׁכְּבָר בָּטֵל נִיסּוּךְ הַמַּיִם שָׁתְקוּ אָמַר לָהֶן בָּנַי בּוֹאוּ וְאוֹמַר לָכֶם שֶׁלֹּא לְהִתְאַבֵּל כׇּל עִיקָּר אִי אֶפְשָׁר שֶׁכְּבָר נִגְזְרָה גְּזֵרָה וּלְהִתְאַבֵּל יוֹתֵר מִדַּאי אִי אֶפְשָׁר שֶׁאֵין גּוֹזְרִין גְּזֵירָה עַל הַצִּבּוּר אֶלָּא אִם כֵּן רוֹב צִבּוּר יְכוֹלִין לַעֲמוֹד בָּהּ דִּכְתִיב בַּמְּאֵרָה אַתֶּם נֵאָרִים וְאֹתִי אַתֶּם קֹבְעִים הַגּוֹי כֻּלּוֹ אֶלָּא כָּךְ אָמְרוּ חֲכָמִים סָד אָדָם אֶת בֵּיתוֹ בְּסִיד וּמְשַׁיֵּיר בּוֹ דָּבָר מוּעָט וְכַמָּה אָמַר רַב יוֹסֵף אַמָּה עַל אַמָּה אָמַר רַב חִסְדָּא כְּנֶגֶד הַפֶּתַח עוֹשֶׂה אָדָם כׇּל צׇרְכֵי סְעוּדָה וּמְשַׁיֵּיר דָּבָר מוּעָט מַאי הִיא אָמַר רַב פָּפָּא כָּסָא דְהַרְסָנָא עוֹשָׂה אִשָּׁה כׇּל תַּכְשִׁיטֶיהָ וּמְשַׁיֶּירֶת דָּבָר מוּעָט מַאי הִיא אָמַר רַב בַּת צִדְעָא שֶׁנֶּאֱמַר אִם אֶשְׁכָּחֵךְ יְרוּשָׁלִָם תִּשְׁכַּח יְמִינִי תִּדְבַּק לְשׁוֹנִי לְחִכִּי וְגוֹ׳

When the Temple was destroyed a second time, there was an increase in the number of ascetics among the Jews, whose practice was to not eat meat and to not drink wine. Rabbi Yehoshua joined them to discuss their practice.

He said to them: My children, for what reason do you not eat meat and do you not drink wine?

They said to him: Shall we eat meat, from which offerings are sacrificed upon the altar, and now the altar has ceased to exist? Shall we drink wine, which is poured as a libation upon the altar, and now the altar has ceased to exist?

Rabbi Yehoshua said to them: If so, we will not eat bread either, since the meal-offerings that were offered upon the altar have ceased.

They replied: You are correct. It is possible to subsist with produce.

He said to them: We will not eat produce either, since the bringing of the first fruits have ceased.

They replied: You are correct. We will no longer eat the produce of the seven species from which the first fruits were brought, as it is possible to subsist with other produce.

He said to them: If so, we will not drink water, since the water libation has ceased.

They were silent, as they realized that they could not survive without water.

Rabbi Yehoshua said to them: My children, come, and I will tell you how we should act. To not mourn at all is impossible, as the decree was already issued and the Temple has been destroyed. But to mourn excessively as you are doing is also impossible, as the Sages do not issue a decree upon the public unless a majority of the public is able to abide by it.

Rabbi Yehoshua continues: Rather, this is what the Sages said: A person may plaster his house with plaster, but he must leave over a small amount in it without plaster to remember the destruction of the Temple. The Gemara interjects: And how much is a small amount? Rav Yosef said: One cubit by one cubit. Rav Ḥisda said: This should be opposite the entrance, so that it is visible to all.

The source for these practices is a verse, as it is stated: “If I forget you, Jerusalem, let my right hand forget its cunning. Let my tongue cleave to the roof of my mouth, if I remember you not; if I set not Jerusalem above my highest joy” (Psalms 137:5–6).

Rabbi Kenneth Brander, "Where are You?" The Most Important Question of Tisha b'Av
Rav Soloveitchik explained that when we read the word “Eicha,” we must also read it the first way that it is pronounced in the Bible, when God asks Adam and Chava: “Ayeka”? Where are you? (Genesis 3:9) Eicha – how did this happen? – and Ayeka – where are you? – are intertwined. Because in order to repair the devastation , we must investigate where we are?
Where are we in the treatment of other Jews and other human beings? Where are we in our support of Israel? Where are we in pursuit of unity?
Do we still not recognize that ultimately it was the judgmental hatred and the disrespect between us that caused famine, torture and the final destruction of the second Temple and all of its ramifications? (Yoma 9b)
Where are we in the process of trying to perfect the world, and help bring about the ultimate redemption?
This approach enables us to also mourn things taking place in our lives and in our generation, which are actually extensions of the tragedies that occurred two millennia ago, making the tragedy more relatable.
In the merit of heartfelt mourning over what we have lost and a resolution to prioritize fixing that which we have broken, may we witness the words of our Sages:
כל המתאבל על ירושלים זוכה ורואה בשמחתה
Whoever mourns for Jerusalem will merit and see her future joy. (Taanit 30b)