This contraction (which ChaBaD of Atzilut undergo in order to radiate in Beriah) thus causes the souls in the World of Beriah to be illuminated by a glow of ChaBaD of the Ein Sof (i.e., ChaBaD of Atzilut); it is this contraction that enables them to have some perception of the Ein Sof-light.
וְהִנֵּה, צִמְצוּם זֶה, הִיא סִבַּת הַהֶאָרָה שֶׁמְּאִירוֹת שָׁם חָכְמָה־בִּינָה־דַּעַת שֶׁל אֵין־סוֹף בָּרוּךְ־הוּא לִנְשָׁמוֹת אֵלּוּ בְּעוֹלַם הַבְּרִיאָה.
The created intellectual beings [of Beriah] cannot, however, apprehend ChaBaD as they are (i.e., in all their undimmed intensity) in the World of Atzilut, where the ChaBaD are not contracted to such a great degree as in Beriah.
מַה שֶּׁאֵין כֵּן בַּאֲצִילוּת, שֶׁאֵינָם בִּבְחִינַת צִמְצוּם כָּל כָּךְ, אִי אֶפְשָׁר לִשְׂכָלִים נִבְרָאִים לְקַבֵּל מֵהֶן,
“To such a great degree”—for the very fact of their being sefirot (i.e., individual, defined categories) indicates that ChaBaD are merely contracted, limited manifestations of the undefinable Ein Sof; the degree of contraction, however, is much less than that of Beriah, and therefore, the creatures of Beriah cannot receive intellectual illumination from ChaBaD of Atzilut.
Therefore, their thought cannot grasp there at all, i.e., the thought and intellect of the created beings of Beriah can in no way grasp the light radiating in Atzilut.
וְלָכֵן, "לֵית מַחֲשַׁבְתָּא דִילְהוֹן תְּפִיסָא שָׁם כְּלָל".
For this reason, [Atzilut] is the abode of the great tzaddikim,
לָכֵן הוּא מָדוֹר לַצַּדִּיקִים הַגְּדוֹלִים,
whose service of G-d is far superior even to fear and love derived from understanding and knowing His greatness,
שֶׁעֲבוֹדָתָם הִיא לְמַעְלָה מַּעְלָה אֲפִילוּ מִבְּחִינוֹת דְּחִילוּ וּרְחִימוּ הַנִּמְשָׁכוֹת מִן הַבִּינָה וָדַעַת בִּגְדוּלָּתוֹ יִתְבָּרֵךְ,
just as Atzilut transcends by far the level of the understanding and knowledge of a created being’s intellect.
כְּמוֹ שֶׁעוֹלַם הָאֲצִילוּת הוּא לְמַעְלָה מַּעְלָה מִבְּחִינַת בִּינָה וָדַעַת לְשֵׂכֶל נִבְרָא,
Their service is, rather, on the level of an actual “chariot” of the blessed Ein Sof,
אֶלָּא עֲבוֹדָתָם הָיְתָה בִּבְחִינַת מֶרְכָּבָה מַמָּשׁ לְאֵין־סוֹף בָּרוּךְ־הוּא,
nullifying their very existence before Him and incorporating themselves, and all that they possess, within His light,
וְלִיבָּטֵל אֵלָיו בִּמְצִיאוּת, וּלְהִכָּלֵל בְּאוֹרוֹ יִתְבָּרֵךְ, הֵם וְכָל אֲשֶׁר לָהֶם,
through the observance of the Torah and the mitzvot.
עַל יְדֵי קִיּוּם הַתּוֹרָה וְהַמִּצְוֹת,
Our Sages applied such a description to the Patriarchs, saying that “they themselves constituted the divine chariot,”9 for this was the Patriarchs’ level of service throughout their lives.
עַל דֶּרֶךְ שֶׁאָמְרוּ: "הָאָבוֹת הֵן הֵן הַמֶּרְכָּבָה", וְהַיְינוּ, לְפִי שֶׁכָּל יְמֵיהֶם הָיְתָה זֹאת עֲבוֹדָתָם.
Hence, the Alter Rebbe will now continue, it is only the G-dliness in a “contracted” ChaBaD that creatures of Beriah can grasp and absorb (and even then only to the extent of their limited capacity); the light of ChaBaD in its pristine state, as in Atzilut, is beyond them.