The difference between the higher and lower worlds is with regard to the flow of vitality, which the blessed Ein Sof causes to flow and illumine in a manner of “revelation out of concealment,”

וְהַהֶבְדֵּל שֶׁבֵּין עוֹלָמוֹת עֶלְיוֹנִים וְתַחְתּוֹנִים, הוּא מִצַּד הַמְשָׁכַת הַחַיּוּת אֲשֶׁר אֵין־סוֹף בָּרוּךְ־הוּא מַמְשִׁיךְ וּמֵאִיר בִּבְחִינַת גִּילּוּי מֵהַהֶעְלֵם

The Alter Rebbe will soon conclude that this revelation is intended for the purpose of vitalizing the worlds and their inhabitants, for the vitality of all worlds and creatures derives from the revelation of G-dliness within them. Thus, the difference between the higher and lower worlds lies in the varying degrees of Divine revelation within them.

With regard to “revelation out of concealment,” the Alter Rebbe now states parenthetically that this manner of revelation is one of the reasons why the G-dly vitality found within the worlds is called “light.”

(which is one of the reasons why the influence and flow of this vitality is figuratively called “light”),

[שֶׁזֶּה אֶחָד מֵהַטְּעָמִים שֶׁהַהַשְׁפָּעָה וְהַמְשָׁכַת הַחַיּוּת מְכוּנָּה בְּשֵׁם "אוֹר" עַל דֶּרֶךְ מָשָׁל],

In Kabbalistic literature, the flow and vitality of G-dliness is termed “light” rather than shefa (“flux”), as it is termed in Jewish speculative philosophy (chakirah). “Light” signifies “revelation out of concealment”: previously, the light had been concealed within the luminary, the source of the light, and subsequently, it is drawn forth from this source and is revealed as light. Thus, in the case of “revelation out of concealment,” only a minute illumination of the source is drawn down into a revealed state. Not so with shefa, where it is the actual “flux” and “stream” of the source that flows down and is revealed. Hence the phrase וְשִׁפְעַת מַיִם (“a flow of water”; Job 22:11): the selfsame water that was previously in one place flows to another place.

The abovementioned “revelation out of concealment” of light serves the purpose of:

thereby animating the worlds and the creatures therein.

לְהַחֲיוֹת הָעוֹלָמוֹת וְהַבְּרוּאִים שֶׁבָּהֶם,

Herein lies the difference between the higher and lower worlds:

For the higher worlds receive this vitality and light in a somewhat more revealed form than do the lower,

שֶׁהָעוֹלָמוֹת הָעֶלְיוֹנִים מְקַבְּלִים בִּבְחִינַת גִּילּוּי קְצָת יוֹתֵר מֵהַתַּחְתּוֹנִים,

I.e., even in the higher worlds, this light and vitality is not manifestly revealed.

and all creatures therein—in the higher worlds—receive the revealed aspect of vitality, albeit each according to its capacity and nature,

וְכָל הַבְּרוּאִים שֶׁבָּהֶם מְקַבְּלִים כָּל אֶחָד כְּפִי כֹּחוֹ וּתְכוּנָתוֹ,

Just as in the analogy, each bodily organ receives vitality from the brain according to its “character and nature,” so, too, does the Alter Rebbe state in the analogue that each creature receives its vitality according to its “capacity and nature.” (—Note by the Rebbe.) This means that each being receives vitality according to its capacity to have the life-force and vitality revealed within it and according to the manner in which this vitality is to be revealed, whether as a revelation of intellect and comprehension or in an emotive manner.

(“But this is not to say that the ‘nature’ conceals the revelation; rather, ‘it imbues and illumines it.’”—Note by the Rebbe.)

which is the nature and form of the particular flow with which the blessed Ein Sof imbues and illumines it.

שֶׁהִיא תְּכוּנַת וּבְחִינַת הַמְשָׁכָה הַפְּרָטִית אֲשֶׁר אֵין־סוֹף בָּרוּךְ־הוּא מַמְשִׁיךְ וּמֵאִיר לוֹ;

But the lower worlds and creatures, even the spiritual ones, do not receive the Divine life-force in quite such a revealed form as it is received in the higher worlds,

וְהַתַּחְתּוֹנִים, אֲפִילוּ הָרוּחָנִיִּים, אֵינָם מְקַבְּלִים בִּבְחִינַת גִּילּוּי כָּל כָּךְ,

but only by means of many garments, wherein the blessed Ein Sof invests the vitality and light which He causes to flow and shine on them in order to animate them.

רַק בִּלְבוּשִׁים רַבִּים אֲשֶׁר אֵין־סוֹף בָּרוּךְ־הוּא מַלְבִּישׁ בָּהֶם הַחַיּוּת וְהָאוֹר אֲשֶׁר מַמְשִׁיךְ וּמֵאִיר לָהֶם לְהַחֲיוֹתָם.

The Divine life-force is garbed in many garments so as not to be revealed. This concealment involves not only a multitudinous profusion of garments—a quantitative manner of concealment—but a qualitative one as well: There is a vast difference between the insubstantial garments that conceal the vitality in the higher worlds and the much denser garments necessary to conceal the G-dly vitality to the degree that creation of the physical becomes possible.