Tanya chapter 1 defines the nefesh habehamit and describes its elemental drives and rootedness in the kelipah. This is foundational for understanding what it means to refine or redirect the animal soul's middot.
אַךְ בֵּיאוּר הָעִנְיָן, עַל פִּי מַה שֶּׁכָּתַב הָרַב חַיִּים וִיטַאל זִכְרוֹנוֹ לִבְרָכָה בְּשַׁעַר הַקְּדוּשָּׁה [וּבְעֵץ חַיִּים שַׁעַר נ׳ פֶּרֶק ב׳], דִּלְכָל אִישׁ יִשְׂרָאֵל, אֶחָד צַדִּיק וְאֶחָד רָשָׁע, יֵשׁ שְׁתֵּי נְשָׁמוֹת, דִכְתִיב: ״וּנְשָׁמוֹת אֲנִי עָשִׂיתִי״, שֶׁהֵן שְׁתֵּי נְפָשׁוֹת –נֶפֶשׁ אַחַת מִצַּד הַקְּלִיפָּה וְסִטְרָא אָחֳרָא, וְהִיא הַמִּתְלַבֶּשֶׁת בְּדַם הָאָדָם לְהַחֲיוֹת הַגּוּף, וּכְדִכְתִיב: ״כִּי נֶפֶשׁ הַבָּשָׂר בַּדָּם הִיא״, וּמִמֶּנָּה בָּאוֹת כָּל הַמִּדּוֹת רָעוֹת, מֵאַרְבַּע יְסוֹדוֹת רָעִים שֶׁבָּהּ, דְּהַיְינוּ: כַּעַס וְגַאֲוָה – מִיסוֹד הָאֵשׁ שֶׁנִּגְבָּהּ לְמַעְלָה, וְתַאֲוַת הַתַּעֲנוּגִים – מִיסוֹד הַמַּיִם, כִּי הַמַּיִם מַצְמִיחִים כָּל מִינֵי תַּעֲנוּג, וְהוֹלֵלוּת וְלֵיצָנוּת וְהִתְפָּאֲרוּת וּדְבָרִים בְּטֵלִים – מִיסוֹד הָרוּחַ, וְעַצְלוּת וְעַצְבוּת – מִיסוֹד הֶעָפָר. וְגַם מִדּוֹת טוֹבוֹת שֶׁבְּטֶבַע כָּל יִשְׂרָאֵל בְּתוֹלְדוֹתָם, כְּמוֹ רַחֲמָנוּת וּגְמִילוּת חֲסָדִים – בָּאוֹת מִמֶּנָּה.
The explanation [of the questions raised above] is to be found in the light of what Rabbi Chaim Vital wrote in Shaar HaKedushah [and in Etz Chaim, Portal 50, ch. 2] that in every Jew, whether righteous or wicked, are two souls, as it is written, “The neshamot (souls) which I have made,” [alluding to] two souls. There is one soul which originates in the kelipah and sitra achara, [and] which is clothed in the blood of a human being, giving life to the body, as is written, “For the life of the flesh is in the blood.” From it stem all the evil characteristics deriving from the four evil elements which are contained in it. These are: anger and pride, which emanate from the element of Fire, the nature of which is to rise upward; the appetite for pleasures—from the element of Water, for water makes to grow all kinds of enjoyment; frivolity and scoffing, boasting and idle talk from the element of Air; and sloth and melancholy—from the element of Earth. From this soul stems also the good characteristics which are to be found in the innate nature of all Israel, such as mercy and benevolence.