Our Rabbis have taught: When Israel is in trouble and one of them separates himself from them, then the two ministering angels who accompany every man come and place their hands upon his head and say, ‘So-and-so who separated himself from the community shall not behold the consolation of the community’. Another [Baraitha] taught: When the community is in trouble let not a man say, ‘I will go to my house and I will eat and drink and all will be well with me’. For of him who does so Scripture says, And behold joy and gladness, slaying oxen and killing sheep, eating flesh and drinking wine — ‘Let us eat and drink, for to-morrow we shall die’. What follows after this [verse]? — And the Lord of Hosts revealed Himself in mine ears; surely this iniquity shall not be expiated by you till ye die.
(ו) וְאֵלּוּ הֵן שֶׁאֵין לָהֶן חֵלֶק לָעוֹלָם הַבָּא אֶלָּא נִכְרָתִים וְאוֹבְדִין וְנִדּוֹנִין עַל גֹּדֶל רִשְׁעָם וְחַטָּאתָם לְעוֹלָם וּלְעוֹלְמֵי עוֹלָמִים. הַמִּינִים. וְהָאֶפִּיקוֹרוֹסִין. וְהַכּוֹפְרִים בַּתּוֹרָה. וְהַכּוֹפְרִים בִּתְחִיַּת הַמֵּתִים וּבְבִיאַת הַגּוֹאֵל. הַמּוֹרְדִים. וּמַחֲטִיאֵי הָרַבִּים. וְהַפּוֹרְשִׁין מִדַּרְכֵי צִבּוּר. וְהָעוֹשֶׂה עֲבֵרוֹת בְּיָד רָמָה בְּפַרְהֶסְיָא כִּיהוֹיָקִים. וְהַמּוֹסְרִים. וּמַטִּילֵי אֵימָה עַל הַצִּבּוּר שֶׁלֹּא לְשֵׁם שָׁמַיִם. וְשׁוֹפְכֵי דָּמִים. וּבַעֲלֵי לָשׁוֹן הָרַע. וְהַמּוֹשֵׁךְ עָרְלָתוֹ:
(6) The following are the people who have no share in the World to Come, but are cut off and lost and judged for the magnitude of their wickedness and sins forever and ever: Sectarians; Heretics; Deniers of Torah; Deniers of Resurrection; [Deniers] of the coming of the Messiah; Apostates; those who lead the masses into sin; those who separate from the community; those who separate from the ways of the community; those who sin with a high hand in public like Jehoiakim; Collaborators [with the government]; those who bring fear upon the community but not for the sake of Heaven; Murderers; Gossipers; and those who reverse their circumcision.
Our Rabbis taught: If at the present time a man desires to become a proselyte, he is to be addressed as follows: ‘What reason have you for desiring to become a proselyte; do you not know that Israel at the present time are persecuted and oppressed, despised, harassed and overcome by afflictions’?
Rav Aharon Lichtenstein ZT"L, Brother Daniel and the Jewish Fraternity
There are deeper implications here, and I think they are clear. The ger cannot embrace Judaism without simultaneously becoming a meber of the Jewish people. He cannot, that is, accept the spiritual aspect of Jewry without the material. And we must go a step further. Rabbi Yehuda laid down the view - later generally accepted - that a proselyte's prayers may refer to the patriarchs as "our fathers" even though he is not their descendant. The reason given is that the Torah describes Avraham as "av hamon goyim," the father of a multitude of nations...To put it in more general terms, the proselyte embraces embraces not only Jewry's present fortunes but its history as well.
Ahabah the son of R. Zera learnt: Any blessing which one has already recited on behalf of himself, he can recite again on behalf of others, save the blessing over bread and the blessing over wine. These if he has not yet recited on behalf of himself he may recite on behalf of others, but if he has already recited them for himself he cannot recite them on behalf of others.
ריטב"א ראש השנה כט עמוד א
שאע"פ שהמצות מוטלות על כל אחד הרי כל ישראל ערבין זה לזה וכולם כגוף אחד וכערב הפורע חוב חבירו.
Ritva Rosh Hashanah 29a
Because even though the commandments are placed upon each individual, all Jews are guarantors of one another, and they are all a single body, and it is like a guarantor who repays the debt of his friend.
כתיב לא תקום ולא תטור את בני עמך. היך עבידא הוה מקטע קופד ומחת סכינא לידוי תחזור ותמחי לידיה.
It states "You shall not take vengeance or bear a grudge against the children of your nation." What is the scenario? He was chopping meat and the knife cut off his hand, would he return and cut off the [other] hand?
Rav Soloveitchik, Kol Dodi Dofek
A preacher of the last generation put it well: He said that the Jewish people may be compared to the man with two heads, concerning whom the question was posed in the house of study: How is he to be viewed for purposes of inheritance? Does he take two portions as a dual person? Or does he take one portion like a single, unified individual...
The answer - the preacher continued - to the question of the unity of the Jewish people is identical with the ruling issued in the house of study regarding the question of the unity of the two-headed heir. Let boiling water be poured on one of his two heads, stated the judge, and let us see the reaction of the other head. If the other head cries out in pain, then both heads blend into one complete and unified personality, and the heir will take one portion. However, if the second head does not feel the pang of the first head, then we have two personalities coupled in one body, and they take two portions.
The same holds true with regard to the question of the unity of the Jewish people. The authoritative ruling is that as long as there is shared suffering, in the manner of "I will be with him in trouble" (Psalms 91:5), there is unity. If the Jew upon whom divine providence has shed a beneficent light, and who consequently believes that, at least with respect to him, the venom of hate and rejection has been expunged from his surroundings, still feels the troubles of his people and the burden of a fate-laden existence, then his link with the people has not been broken. If boiling water is poured upon the head of the Jew in Morocco, the fashionably-attired Jew in London or Paris has to scream at the top of his voice, and through feeling the pain he will remain faithful to his people. The fragmentation of the people and the blearing of its image are concomitants of the absence of the feeling of sympathy.
העמק דבר דברים לב:ח
ולפי דרכינו המשל כמו חבל עב שיש בו רבבות אלפי חוטים דקים ולמעלה המה מפותלים יפה ולמטה הם נפרדים כל חוט בפני עצמו, כך הקדוש ברוך הוא כביכול הוא ית׳ נשמתא דנשמתין, וכל נשמות ישראל למעלה מקושרים המה, ולמטה לכל אחד נשמה בפני עצמו, ומשום הכי נקראו ישראל גוי אחד שמאוחדים המה בשרשן למעלה.
Emek Davar Devarim 32:8
And according to our approach the parable is like a thick rope that contains tens of thousands of thin strands. Above them is well intertwined, and below they are separated into individual strands. Similarly, Hashem at is were is the ultimate soul, and all souls of Jews are bound up together, and below each one is an individual soul. And for this reason Jews are called "one nation," for they are unified in their root above.
Tanya, Chapter 32
Acting on the suggestion mentioned above— to view one's body with scorn and contempt, and finding joy only in the joy of the soul alone— is a direct and easy way to attain the fulfillment of the commandment "Thou shalt love thy fellow as thyself" toward every soul of Israel, both great and small.
For, whereas one despises and loathes one's body, while as for the soul and spirit, who can know their greatness and excellence in their root and source in the living G-d? Being, moreover, all of a kind and all having one Father— therefore, all Israelites are called real brothers by virtue of the source of their souls in the One G-d; only the bodies are separated. Hence in the case of those who give major consideration to their bodies while regarding their souls as of secondary importance, there can be no true love and brotherhood among them, but only [a love] which is dependent on a [transitory] thing.
This is what Hillel the Elder meant when he said in regard to the fulfillment of this commandment, "This is the whole Torah, whilst the rest is but commentary," and so on.