Children are you to YHVH your God! You are not to gash yourselves, you are not to put a bald-spot between your eyes for a dead-person.
(י) לא תתגודדו. (יבמות יג) לא תעשו אגודות [אגודות], אלא היו כלכם אגודה אחת. וכן הוא אומר (עמוס ט): ואגודתו על ארץ יסדה.
(10) (Devarim, Ibid.) "Do not lacerate yourselves" (lo tithgodedu): Do not form opposing factions (agudoth, agudoth), but all of you consolidate into one bond, as in (Amos 9:6) "and He founded His bond (agudah) upon the earth."
(יד) וּבִכְלַל אַזְהָרָה זֶה שֶׁלֹּא יִהְיוּ שְׁנֵי בָּתֵּי דִּינִין בְּעִיר אַחַת זֶה נוֹהֵג כְּמִנְהָג זֶה וְזֶה נוֹהֵג כְּמִנְהָג אַחֵר. שֶׁדָּבָר זֶה גּוֹרֵם לְמַחֲלוֹקוֹת גְּדוֹלוֹת שֶׁנֶּאֱמַר (דברים יד א) "לֹא תִתְגֹּדְדוּ" לֹא תֵּעָשׂוּ אֲגֻדּוֹת אֲגֻדּוֹת:
(14) Included in this prohibitive commandment is also a warning that there shall not be two tribunals in one city, one following one set of customs and the other following another set of customs, for such practice causes great divisions, even as it is said: "Ye shall not cut (divide) yourselves" (Ibid.), ye shall not multiply divisions.17Yebamot, 13b. C.
(ב) רַבִּי חָמָא בַּר חֲנִינָא פָּתַח (משלי כז, יז): בַּרְזֶל בְּבַרְזֶל יָחַד, אָמַר רַבִּי חָמָא בַּר חֲנִינָא אֵין סַכִּין מִתְחַדֶּדֶת אֶלָּא בְּיָרֵךְ שֶׁל חֲבֶרְתָּהּ, כָּךְ אֵין תַּלְמִיד חָכָם מִתְחַדֵּד אֶלָּא בַּחֲבֵרוֹ, בַּרְזֶל בְּבַרְזֶל יָחַד וְאִישׁ יַחַד פְּנֵי רֵעֵהוּ, אִישׁ זֶה יַעֲקֹב, כֵּיוָן שֶׁעָמַד אָבִינוּ יַעֲקֹב אִישׁ יַחַד פְּנֵי רֵעֵהוּ, שֶׁנִּתְיַחֲדָה עָלָיו הַשְּׁכִינָה, וְהִנֵּה ה' נִצָּב עָלָיו.
(2) Rabbi Chama Bar Chanina opened with the following verse: Iron sharpens iron (Proverbs 27:17). Rabbi Chama Bar Chanina said: A knife will only become sharpened only at the side of another. So too, a Torah scholar can only become sharpened by a friend. "Iron sharpens iron and a person sharpens the face of his neighbor." This is referring to Jacob. When our father Jacob stood together (play on sharpened) with his friend, the Shekinah attached itself (or sharpened) to him. As it says "Behold Adonai stood upon him" (Genesis 38:13).
הִלֵּל אוֹמֵר, אַל תִּפְרֹשׁ מִן הַצִּבּוּר, וְאַל תַּאֲמִין בְּעַצְמְךָ עַד יוֹם מוֹתְךָ, וְאַל תָּדִין אֶת חֲבֵרְךָ עַד שֶׁתַּגִּיעַ לִמְקוֹמוֹ, וְאַל תֹּאמַר דָּבָר שֶׁאִי אֶפְשָׁר לִשְׁמֹעַ, שֶׁסּוֹפוֹ לְהִשָּׁמַע. וְאַל תֹּאמַר לִכְשֶׁאִפָּנֶה אֶשְׁנֶה, שֶׁמָּא לֹא תִפָּנֶה:
(4) Hillel says: Do not separate yourself from the community. Do not believe in yourself until the day of your death. Do not judge your fellow until you come to his place. Do not say something that cannot be heard, for in the end it will be heard. Do not say, "When I will be available I will study [Torah]," lest you never become available.
מקדש ראשון מפני מה חרב מפני ג' דברים שהיו בו ע"ז וגלוי עריות ושפיכות דמים ע"ז דכתיב (ישעיהו כח, כ) כי קצר המצע מהשתרע מאי קצר המצע מהשתרע . . . . אבל מקדש שני שהיו עוסקין בתורה ובמצות וגמילות חסדים מפני מה חרב מפני שהיתה בו שנאת חנם ללמדך ששקולה שנאת חנם כנגד שלש עבירות ע"ז גלוי עריות ושפיכות דמים
§ The Tosefta continues with a discussion of the sins of the Jewish people over the generations: Due to what reason was the First Temple destroyed? It was destroyed due to the fact that there were three matters that existed in the First Temple: Idol worship, forbidden sexual relations, and bloodshed. . . . .However, considering that the people during the Second Temple period were engaged in Torah study, observance of mitzvot, and acts of kindness, and that they did not perform the sinful acts that were performed in the First Temple, why was the Second Temple destroyed? It was destroyed due to the fact that there was wanton hatred during that period. This comes to teach you that the sin of wanton hatred is equivalent to the three severe transgressions: Idol worship, forbidden sexual relations and bloodshed.