Daf 139a (דַּף קַל״ט ע״א)

And for this reason (וּבְגִין כָּךְ), Yisrael must anticipate and be wise toward him with Chokhmah, with crookedness (יִשְׂרָאֵל מְקַדְּמִין וְחַכְּמִין לֵיהּ בְּחָכְמָה, בְּעֲקִימוּ), so that he will not be able to deceive and dominate (בְּגִין דְּלָא יָכִיל לְאַבְאָשָׁא וּלְשַׁלְטָאָה). And therefore Ya'akov, who is in the secret of faith (וְעַל דָּא יַעֲקֹב דְּאִיהוּ בְּרָזָא דִמְהֵימְנוּתָא), all his deeds toward Esav were in order that he not give place to that Serpent (כָּל עוֹבָדוֹי לְגַבֵּי דְעֵשָׂו בְּגִין דְּלָא יָהַב דּוּכְתָּא לֵיהּ לְהַהוּא חִוְיָא), to defile the Mikdash (לְסָאֲבָא מַקְדְּשָׁא), and not to approach it, and not to rule in the world (וְלָא יַקְרִיב לְגַבֵּיהּ, וְלָא יִשְׁלוֹט בְּעַלְמָא). And for this reason it was not necessary for Avraham to conduct himself in crookedness (וְעַל דָּא לָא אִצְטְרִיךְ לֵיהּ לְאַבְרָהָם לְאִתְנַהֲגָא בְּעוּקְמָא), nor for Yitzchak (וְלָא לְיִצְחָק), because Esav, who is the side of that Serpent, had not yet entered the world (בְּגִין דְּעֵשָׂו דְּאִיהוּ סִטְרָא דְּהַהוּא חִוְיָא, עַד לָא אֲתָא לְעַלְמָא). But Ya'akov, who is the master of the House (אֲבָל יַעֲקֹב, דְּאִיהוּ מָארֵיהּ דְּבֵיתָא), had to stand up against that Serpent (אִיבָּעֵי לֵיהּ לְקָיְימָא לְקֳבְלֵיהּ דְּהַהוּא חִוְיָא), so that he would not grant him dominion at all to defile the Temple of Ya'akov (דְּלָא יָהִיב לֵיהּ שָׁלְטָנוּתָא כְּלָל לְסָאֲבָא בֵּי מַקְדְּשָׁא דְיַעֲקֹב). And for this reason, Ya'akov was required more than all the people of the world (וְעַל דָּא אִצְטְרִיךְ לְיַעֲקֹב יַתִּיר מִכָּל בְּנֵי עַלְמָא). And therefore, Yisrael the holy ones were clarified as a portion from Kudsha Berikh Hu (וּבְגִין כָּךְ יִשְׂרָאֵל קַדִּישִׁין אִתְבְּרִירוּ חוּלַק עַדְבֵיהּ דְּקוּדְשָׁא בְּרִיךְ הוּא), as it is written, “For Hashem’s portion is His people; Ya'akov is the lot of His inheritance” (Deuteronomy 32) (דִּכְתִיב כִּי חֵלֶק יְיָ עַמּוֹ יַעֲקֹב חֶבֶל נַחֲלָתוֹ). “And the boys grew up” (Bereshit 25) (וַיִּגְדְּלוּ הַנְּעָרִים)-the side of Avraham caused them to grow, and his merit aided them (סִטְרָא דְאַבְרָהָם גָּרִים לוֹן לְאִתְגַּדָּלָא וּזְכוּתֵיהּ סִיַּיע לוֹן), for he was educating them in the commandments (הוּא הֲוָה מְחַנֵּךְ לוֹן בְּמִצְוֹת), as it is written, “For I know him, that he will command his children…” (Bereshit 18) (דִּכְתִיב כִּי יְדַעְתִּיו לְמַעַן אֲשֶׁר יְצַוֶּה אֶת בָּנָיו וְגו׳), in order to elevate Ya'akov and Esav (לְאַסְגָּאָה יַעֲקֹב וְעֵשָׂו). “And the boys grew up, and Esav was a man who knew hunting…” (Bereshit 25) (וַיִּגְדְּלוּ הַנְּעָרִים וַיְהִי עֵשָׂו אִישׁ יוֹדֵעַ צַיִד וְגו׳). Rabbi El'azar said (אָמַר רִבִּי אֶלְעָזָר), each one separated to his path (כָּל חַד וְחַד אִתְפְּרַשׁ לְאָרְחֵיהּ), this one to the side of faith (דָּא לְסִטְרָא דִמְהֵימְנוּתָא), and this one to the side of idolatry (וְדָא לְסִטְרָא דְּעֲבוֹדָה זָרָה).