The Alter Rebbe explains that on Shabbat an additional, higher light of holiness shines into the Jewish neshama, elevating it beyond its weekday state; Shabbat is thus described as the primary occasion of divine nourishment for the soul.
״וְאֶת רוּחַ הַטּוּמְאָה אַעֲבִיר מִן הָאָרֶץ״ – דְּלָא יִתְפַּרְנְסוּן תַּלְמִידֵי חֲכָמִים מֵעַמֵּי הָאָרֶץ, אֶלָּא, מִסִּטְרָא דְטוֹב – דְּאָכְלִין טָהֳרָה, כָּשֵׁר, הֶיתֵּר, וְלָא מֵ״עֵרֶב רַב״ דְּאָכְלִין טוּמְאָה, פָּסוּל, אָסוּר כוּ׳, וּבְזִמְנָא דְּאִילָנָא דְטוֹב וָרָע שָׁלְטָא כוּ׳, אִינוּן חֲכָמִים דְּדַמְיָין לְשַׁבָּתוֹת וְיָמִים טוֹבִים, לֵית לְהוֹן אֶלָּא מַה דְיָהֲבִין לְהוֹן אִינּוּן ״חוּלִּין״, כְּגַוְונָא דְּיוֹם הַשַּׁבָּת, דְּלֵית לֵיהּ אֶלָּא מַה דִמְתַקְּנִין לֵיהּ בְּיוֹמָא דְחוֹל.
There, there is no question from the side of evil and no disagreement from the spirit of impurity, as it is written: ‘And the spirit of impurity I shall remove from the earth.’ Thus the scholars of Torah will no longer be sustained by illiterate persons (amey haaretz), but from the side of the good, by those who consume what is pure, kosher permitted; nor by the mixed multitude (erev rav)—who consume what is impure, unfit, prohibited…. But while the Tree of Good and Evil domineers…, these Sages, who are compared to Shabbat and Festivals, have nothing save what is given to them by those profane ones, analogous to the day of Shabbat which has but what has been prepared for it on a weekday.