The Alter Rebbe (R. Shneur Zalman of Liadi) explains that all physical existence, including food, is continuously created and sustained by divine speech (dibur); the manna, which came directly from God's word, reveals the hidden truth that underlies all sustenance — that 'man lives by every utterance of God.'
וּבֵיאוּר הָעִנְיָן, הוּא רַק אֱמוּנָה אֲמִיתִּית בְּ״יוֹצֵר בְּרֵאשִׁית״, דְּהַיְינוּ, שֶׁהַבְּרִיאָה ״יֵשׁ״ מֵ״אַיִן״, הַנִּקְרֵאת ״רֵאשִׁית חָכְמָה״ – וְהִיא חָכְמָתוֹ שֶׁאֵינָהּ מוּשֶּׂגֶת לְשׁוּם נִבְרָא – הַבְּרִיאָה הַזֹּאת, הִיא בְּכָל עֵת וָרֶגַע, שֶׁמִּתְהַוִּים כָּל הַבְּרוּאִים ״יֵשׁ״ מֵ״אַיִן״ מֵחָכְמָתוֹ יִתְבָּרֵךְ הַמְחַיָּה אֶת הַכֹּל, וּכְשֶׁיִּתְבּוֹנֵן הָאָדָם בְּעוֹמֶק הֲבָנָתוֹ, וִיצַיֵּיר בְּדַעְתּוֹ הֲוָויָיתוֹ מֵ״אַיִן״ בְּכָל רֶגַע וָרֶגַע מַמָּשׁ, הַאֵיךְ יַעֲלֶה עַל דַּעְתּוֹ כִּי רַע לוֹ, אוֹ שׁוּם יִסּוּרִים מִבָּנֵי חַיֵּי וּמְזוֹנֵי, אוֹ שְׁאָרֵי יִסּוּרִין בָּעוֹלָם, הֲרֵי הָ״אַיִן״, שֶׁהִיא חָכְמָתוֹ יִתְבָּרֵךְ, הוּא מְקוֹר הַחַיִּים וְהַטּוֹב וְהָעוֹנֶג, וְהוּא הָעֵדֶן שֶׁלְּמַעְלָה מֵעוֹלָם־הַבָּא, רַק, מִפְּנֵי שֶׁאֵינוֹ מוּשָּׂג, לָכֵן נִדְמֶה לוֹ רַע אוֹ יִסּוּרִים, אֲבָל בֶּאֱמֶת אֵין רַע יוֹרֵד מִלְמַעְלָה, וְהַכֹּל טוֹב, רַק שֶׁאֵינוֹ מוּשָּׂג לְגוֹדְלוֹ וְרַב טוּבוֹ. וְזֶהוּ עִיקַּר הָאֱמוּנָה שֶׁבִּשְׁבִילָהּ נִבְרָא הָאָדָם, לְהַאֲמִין דְּ״לֵית אֲתַר פָּנוּי מִינֵיהּ״, וּ״בְאוֹר פְּנֵי מֶלֶךְ חַיִּים״, וְעַל כֵּן ״עוֹז וְחֶדְוָה בִּמְקוֹמוֹ״ – הוֹאִיל וְהוּא רַק טוֹב כָּל הַיּוֹם.
This means: There is to be only an absolute belief in the Yotzer Bereishit; that is, that the creation of being ex nihilo (yesh meayin) [which is called reishit chochmah, i.e., His wisdom which is not apprehensible to any creature]—this creation occurs constantly and every moment, by all creatures coming into being [as a substance ex nihilo (yesh meayin)] from His wisdom, blessed be He, which animates everything. And when man will contemplate in the profundity of his understanding, and will imagine in his mind his coming to be ex nihilo—truly every moment, how can he possibly think he has ever suffered, or had any afflictions related to “children, life, and sustenance,” or whatever other worldly sufferings. For the naught (ayin) which is His wisdom, blessed be He, is the source of life, welfare, and delight. It is the Eden which transcends the World to Come, except that, because it is not apprehensible, one imagines to have sufferings, or afflictions. In fact, however, no evil descends from above and everything is good, though it is not apprehended because of its immense and abundant goodness. And this is the essence of the faith for which man was created: to believe that “there is no place void of Him” and “in the light of the King’s Countenance there is life,” and, conclusively, “strength and gladness are in His place,” because He is but good all the time.