Until now, the Alter Rebbe has mentioned mainly the 248 organs of the body and the corresponding 248 functional powers of the soul enclothed within them. Now, however, he goes into more detail, referring to all 613 functional powers, both those of the 248 organs and those of the 365 blood vessels, each of which has its own, unique life-force from the soul. This explains why he now refers to 613 rather than 248.

Now, concerning the flow of all the 613 kinds of functional powers and vital forces which are drawn from the concealment of the soul, where they are previously hidden and from where they are now drawn to the body to animate it—

וְהִנֵּה, עַל הַמְשָׁכַת כָּל הַתַּרְיַ"ג מִינֵי כֹּחוֹת וְחַיּוּת מֵהֶעְלֵם הַנְּשָׁמָה אֶל הַגּוּף לְהַחֲיוֹתוֹ –

concerning this flow, [the Sages] have said that the principal dwelling place and abode of this flow and revelation of the previously concealed powers and forces is entirely situated in the brains of the head.

עָלֶיהָ אָמְרוּ, שֶׁעִיקַּר מִשְׁכָּנָהּ וְהַשְׁרָאָתָהּ שֶׁל הַמְשָׁכָה זוֹ וְגִילּוּי זֶה – הוּא כּוּלּוֹ בַּמּוֹחִין שֶׁבָּרֹאשׁ,

Therefore, it is they, the brains, which first receive the power and life-force appropriate to them according to their composition and character—namely, intellect which is divided into the three intellectual faculties called ChaBaD (chochmah, binah, daat), and the faculty of thought, and whatever pertains to the brain. All these receive their life-force from the soul before the other parts of the body.

וְלָכֵן הֵם מְקַבְּלִים תְּחִלָּה הַכֹּחַ וְהַחַיּוּת הָרָאוּי לָהֶם לְפִי מִזְגָּם וּתְכוּנָתָם, שֶׁהֵן חָכְמָה־בִּינָה־דַּעַת וְכֹחַ הַמַּחֲשָׁבָה וְכָל הַשַּׁיָּיךְ לַמּוֹחִין.

And not only this—that the brains receive their own life-force before the other organs—but also the overall flow of all the individual streams of vitality to the other organs is also first included and enclothed in the brains of the head before it becomes revealed in the individual organs,

וְלֹא זוֹ בִּלְבָד, אֶלָּא גַּם כְּלָלוּת כָּל הַמְשָׁכוֹת הַחַיּוּת לִשְׁאָר הָאֵבָרִים, גַּם כֵּן כְּלוּלָה וּמְלוּבֶּשֶׁת בַּמּוֹחִין שֶׁבָּרֹאשׁ,

and it is there, in the brain, that the core and source of the said flow exist in a form in which the light and vitality of the entire soul are revealed. In other words, when the general flow of vitality reaches the brain, then the “light” and vitality of the entire body begin to be revealed.

וְשָׁם הוּא עִיקָּרָהּ וְשָׁרְשָׁהּ שֶׁל הַמְשָׁכָה זוֹ, בִּבְחִינַת גִּילּוּי הָאוֹר וְהַחַיּוּת שֶׁל כָּל הַנְּשָׁמָה כוּלָּהּ,

From there, the brain, radiance flows to all the other organs, each of which then receives the functional power and vital force appropriate to it according to its composition and character: the power of sight is revealed in the eye, the power of hearing in the ear, and so on.

וּמִשָּׁם מִתְפַּשֶּׁטֶת הֶאָרָה לִשְׁאָר כָּל הָאֵבָרִים, וּמְקַבֵּל כָּל אֶחָד כֹּחַ וְחַיוּת הָרָאוּי לוֹ כְּפִי מִזְגּוֹ וּתְכוּנָתוֹ: כֹּחַ הָרְאִיָּה מִתְגַּלֶּה בָּעַיִן, וְכֹחַ הַשְּׁמִיעָה בָּאוֹזֶן וְכוּ'.

In other words: At which point does a power of sight come into existence, ready to be revealed in the eye, and a power of hearing in the ear? Only after the overall life-force of the whole body is drawn into the brain in a general manner, then a “radiance” is drawn from there to each organ, a radiance which is already constituted in accordance with the particular character of the individual organ.

But all functional powers flow from the brain, as is known,4 for there, in the brain, is located the principal dwelling place of the entire soul, in a revealed form,

וְכָל הַכֹּחוֹת מִתְפַּשְּׁטִים מֵהַמּוֹחַ כַּנּוֹדָע, כִּי שָׁם הוּא עִיקַּר מִשְׁכַּן הַנְּשָׁמָה כוּלָּהּ בִּבְחִינַת גִּילּוּי,

Although the soul actually exists all over the body equally, with no difference between one organ and another, yet the principal place in which the soul is revealed is in the brain.

since there, in the brain, the overall life-force which flows from the soul is revealed. It is only the individual faculties of the overall life-force which shine forth and radiate from there, the brain, to all the organs of the body, just as light radiates and shines from the sun into the innermost of rooms.

שֶׁנִּגְלֵית שָׁם כְּלָלוּת הַחַיּוּת הַמִּתְפַּשֵּׁט מִמֶּנָּה. רַק כֹּחוֹתֶיהָ שֶׁל כְּלָלוּת הַחַיּוּת מְאִירִים וּמִתְפַּשְּׁטִים מִשָּׁם לְכָל אֵבְרֵי הַגּוּף, כְּדִמְיוֹן הָאוֹר הַמִּתְפַּשֵּׁט וּמֵאִיר מֵהַשֶּׁמֶשׁ לְחַדְרֵי חֲדָרִים.

(5Even the heart, which is a central organ from which all other organs receive vitality—“The heart diffuses to all organs”—receives its own vital force from the brain, which is why the brain naturally dominates the heart, as explained above.)

[וַאֲפִילוּ הַלֵּב – מְקַבֵּל מֵהַמּוֹחַ, וְלָכֵן הַמּוֹחַ שַׁלִּיט עָלָיו בְּתוֹלַדְתּוֹ, כַּנִּזְכָּר לְעֵיל].

In ch. 12, it was explained that man is created with a natural supremacy of the brain over the heart, and the reason is explained here—because the heart, despite its centrality, must in turn receive its own vital force from the soul through the medium of the brain.