The revelation of the unity among the particular types of Jewsוְעַל יְדֵי גִלּוּי הָאַחְדּוּת בְּהַפְּרָטִים שֶׁבְּיִשְׂרָאֵל
(the four categories mentioned above in sec. 2,(ד' הַסּוּגִים שֶׁבִּכְלַל יִשְׂרָאֵל,
and similarly, the revelation of the unity that exists among the four levels within the soul of every individual Jew),1וְד' הַדַּרְגּוֹת שֶׁבְּנִשְׁמַת כָּל אֶחָד),
makes possible yet another development. The mitzvah of taking the four speciesנִמְשָׁךְ עַל יְדֵי מִצְוַת נְטִילַת ד' מִינִים עוֹד עִנְיָן,
reveals that the Jews prevailed in the judgment of Rosh HaShanahשֶׁעַל יָדָם מִתְגַּלֶּה שֶׁיִּשְׂרָאֵל אִינוּן נִצּוּחַיָּא,
and, moreover, that even the non-Jewish nations accept this judgment,וּבְאוֹפֶן שֶׁגַּם אֻמּוֹת הָעוֹלָם מַסְכִּימִים לָזֶה,
to the extent that they praise and laud G‑dוְעַד שֶׁהֵם מְהַלְלִים וּמְשַׁבְּחִים אֶת הֲוָיָ׳
for having showered upon us His overwhelming kindness.עַל זֶה שֶׁגָּבַר עָלֵינוּ חַסְדּוֹ.
To explain this matter, and to focus on the inner dimension implied by the statement of the Midrash that the non-Jews accept that the Jews prevailed in judgment: Multiplicity is fundamentally relevant with regard to the non-Jewish nations.וְהָעִנְיָן הוּא, דְּעִנְיַן הָרִבּוּי הוּא בְּעִקָּר בְּאֻמּוֹת הָעוֹלָם.
Aside from the fact that “You are the least among the nations,”2דְּנוֹסָף לָזֶה שֶׁאַתֶּם הַמְעַט מִכָּל הָעַמִּים
and the Jewish people are but one of the seventy nations of the world,3וְיִשְׂרָאֵל אֶחָד בְּשִׁבְעִים בָּאֻמּוֹת,
the Jewish people are characterized by singularity: the entire people form one unified entity.4הִנֵּה כָּל יִשְׂרָאֵל הֵם קוֹמָה אַחַת,
In contrast, multiplicity (the existence of separate entities) characterizes non-Jews and the nations of the world.5וְעִנְיַן הָרִבּוּי (דְּבָרִים נִפְרָדִים) הוּא בַגּוֹיִם וְאֻמּוֹת הָעוֹלָם.
The reason that the entire Jewish people is characterized by unity isוְהִנֵּה הַטַּעַם עַל זֶה שֶׁכָּל יִשְׂרָאֵל הֵם בְּאַחְדּוּת הוּא
because their source is G‑d’s name Havayah, of which it is said,6 “Havayah is one.”7מִפְּנֵי שֶׁשָּׁרְשָׁם הוּא בַּהֲוָיָ', הֲוָיָ׳ אֶחָד.
From this, it can be understood that the oneness of the Jewish people is of an essential nature.וּמִזֶּה מוּבָן, דְּעִנְיַן הָאַחְדּוּת דְּיִשְׂרָאֵל הוּא
Not only are they not separate one from the other (as are the other nations);נוֹסָף עַל זֶה שֶׁאֵינָם נִפְרָדִים זֶה מִזֶּה (כְּאֻמּוֹת הָעוֹלָם),
they are above (and stand apart from) the division that characterizes the angels8 and the spiritual realms,אֶלָּא שֶׁהֵם נַעֲלִים (בִּשְׁלִילָה) גַּם מֵהִתְחַלְּקוּת דְּמַלְאָכִים וּדְעוֹלָמוֹת
which derive their existence from G‑d’s name Elokim, a name that employs the plural form and which therefore denotes multiplicity.9שֶׁנִּתְהַוּוּ מִשֵּׁם אֱלֹקִים לְשׁוֹן רַבִּים,
Moreover, they are also above the source for division that exists within G‑d’s name Elokim (as reflected by its plural form).וִיתֵרָה מִזּוֹ, שֶׁהֵם לְמַעְלָה גַּם מֵהַהִתְחַלְּקוּת דְּשֵׁם אֱלֹקִים (לְשׁוֹן רַבִּים),
On the surface, the use of a plural in reference to G‑d is problematic, for G‑d is the Source of all Oneness. Nevertheless, since the world that He brings into being is characterized by division and multiplicity, there exists within G‑d Himself a source for the diverse qualities manifest in creation. (As explained at length in Tanya, Shaar HaYichud VehaEmunah, the existence of this level neither contradicts nor conflicts with G‑d’s essential oneness, for Havayah and Elokim are one.)
As a whole, this refers to G‑d’s light that is memale kol almin, which vitalizes every world in the hierarchy of both the spiritual realms above and also this physical world, relating to every created being on its particular level.שֶׁבִּכְלָלוּת הוּא אוֹר הַמְמַלֵּא כָּל עָלְמִין שֶׁמְּחַיֶּה כָּל עוֹלָם וְכָל נִבְרָא לְפִי עֶרְכּוֹ.
Since this Divine light invests itself in every world and in every created being according to its own level, it must also be characterized by a certain dimension of multiplicity. To allude to this concept, G‑d’s name Elokim, the spiritual source of this entire framework of existence, uses a plural form. The Jewish people, however, are intimately bound up with the essential G‑dliness reflected by the name Havayah, which is characterized by unity and which transcends the entire concept of division.
Nevertheless, there also exists (in the external dimension of their being) an aspect of multiplicity among the Jewish people.אֶלָּא שֶׁאַף-עַל-פִּי-כֵן, כֵּיוָן שֶׁגַּם בְּיִשְׂרָאֵל יֵשׁ עִנְיַן הָרִבּוּי (בְּחִיצוֹנִיּוּת),
Simply put, each Jew possesses a different individual nature than his fellow man. On a larger scale, these differences are reflected in the four types of Jews symbolized by the four species.
By drawing down unity within those aspects of multiplicity that exist among the Jewish people through the mitzvah of taking the four species,הִנֵּה עַל יְדֵי הַמְשָׁכַת הָאַחְדּוּת בְּהָרִבּוּי דְּיִשְׂרָאֵל,
unity is also drawn down into the multiplicity that characterizes G‑d’s name Elokim,עַל יְדֵי זֶה הִיא נִמְשֶׁכֶת גַּם בְּהָרִבּוּי דְּשֵׁם אֱלֹקִים,
and in that way, is drawn down within the multiplicity that characterizes the various worlds, both spiritual and material, and the created beings found within these worlds,וְעַל יְדֵי זֶה גַּם בְּהָרִבּוּי דְּעוֹלָמוֹת וְנִבְרָאִים,
including even the vast multiplicity that characterizes the created beings of this material world.וְעַד לְרִבּוּי הַנִּבְרָאִים שֶׁבָּעוֹלָם הַזֶּה הַגַּשְׁמִי
[For the concept “How manifold are Your works, O G‑d!”10[דְּעִנְיַן מָה רַבּוּ מַעֲשֶׂיךָ ה'
(division into a multitude of individual levels)(הַהִתְחַלְּקוּת לְרִבּוּי פְּרָטִים)
applies primarily in this material world].הוּא בְּעִקָּר בָּעוֹלָם הַזֶּה הַגַּשְׁמִי דַּוְקָא],
This also includes the multitude of non-Jewish nations.כּוֹלֵל גַּם הָרִבּוּי דְּאֻמּוֹת הָעוֹלָם.
It is possible to explain that this is also the connection between the two interpretations of the concept of the four species:וְיֵשׁ לוֹמַר, דְּזֶהוּ הַקֶּשֶׁר דִּשְׁנֵי הַפֵּרוּשִׁים בְּעִנְיָנָם שֶׁל ד' מִינִים,
According to one interpretation, they represent the four categories within the Jewish people,דִּלְפֵרוּשׁ אֶחָד הֵם כְּנֶגֶד ד' סוּגִים שֶׁבְּיִשְׂרָאֵל
whereas according to another interpretation they represent the four supernal rungs of G‑dliness (as stated above in sec. 2).וּלְפֵרוּשׁ אֶחָד הֵם כְּנֶגֶד ד' דַּרְגּוֹת דִּלְמַעְלָה (כַּנִּזְכָּר לְעֵיל סְעִיף ב),
To explain the connection between the two interpretations: The four levels of G‑dly light Above refer to His light that is memale kol almin,דְּעִנְיַן ד' הַדַּרְגּוֹת שֶׁלְּמַעְלָה הוּא שֶׁאוֹר הַמְמַלֵּא כָּל עָלְמִין
the light that grants vitality and brings into being the four worlds of Atzilus, Beriah, Yetzirah, and Asiyah,מְחַיֶּ' וּמְהַוֶּה אֶת ד' הָעוֹלָמוֹת אֲצִילוּת-בְּרִיאָה-יְצִירָה-עֲשִׂיָּה,
each world according to its level.כָּל עוֹלָם לְפִי עֶרְכּוֹ.
Through drawing down unity into the multiplicity that exists within the Jewish people (as they are reflected in the four categories and their four respective levels),וְעַל יְדֵי הַמְשָׁכַת הָאַחְדּוּת בְּהָרִבּוּי (ד' סוּגִים וְד' דַּרְגּוֹת) דְּיִשְׂרָאֵל,
unity is subsequently drawn down into the multiplicity that characterizes G‑d’s light that is memale kol alminעַל יְדֵי זֶה מַמְשִׁיכִים זֶה גַּם בִּבְחִינַת הָרִבּוּי שֶׁבְּאוֹר הַמְמַלֵּא
(the four supernal levels of G‑dly light)(ד' דַּרְגּוֹת דִּלְמַעְלָה),
and in turn also into the multiplicity that characterizes the numerous worlds,וְעַל יְדֵי זֶה – גַּם בְּהָרִבּוּי דְּעוֹלָמוֹת וְכו'
even into the multiplicity that characterizes the nations of this material world.וְעַד בְּהָרִבּוּי דְּאֻמּוֹת הָעוֹלָם.

Summary

The revelation of the unity that exists among the particular types of Jews leads to unity in the world at large, as expressed in the non-Jews’ acceptance of the Jews’ victory in the judgment of Rosh HaShanah.
To explain: Fundamentally, the Jewish people are characterized by unity, since their souls are rooted in G‑d’s name Havayah, which is characterized by oneness. By contrast, the non-Jews derive from G‑d’s name Elokim, which (as reflected by its plural form) is the source of multiplicity. Hence, the non-Jews are characterized by division.
There also exists an aspect of multiplicity within the external dimensions of the Jewish people. By drawing down oneness into those aspects of multiplicity found within the Jewish people through the mitzvah of taking the four species, oneness is subsequently drawn down into the multiplicity that characterizes G‑d’s name Elokim and into all the worlds and created beings that derive from it, including the non-Jewish nations.