One of the other great nissim that occurs in this week's parsha, that of the Manna that fell from Heaven, is meant to teach us the same concept.
The Torah tells us (טז ד) לְמַעַן אֲנַסֶּנּוּ הֲיֵלֵךְ בְּתוֹרָתִי אִם לֹא Hashem told Moshe I will send them food from the Heavens in order to test them whether they go in the ways of the Torah or not. There were certain halachos that the Yidden collecting the manna had to abide by; Hashem was testing whether they were being loyal to the Torah or not. Every man was allowed to take עֹמֶר לַגֻּלְגֹּלֶת an exact amount of manna per member of his household, no more. On Shabbos they were not allowed to gather manna, and so forth.
The Mechilta says in the name of Rabbi Shimon bar Yochai לֹא נִתְּנָה תּוֹרָה לִדְרֹשׁ אֶלָּא לְאוֹכְלֵי הַמָּן - the Torah was only given to be pondered by those that eat the manna. What is the meaning of this statement? Was the Torah not given to the nation that was heading towards Eretz Yisrael where they would eventually work in order to produce food through the toil of their hands?
A Manna Mindset
The seforim tell us what was the message of the manna. When the manna rained down from the skies, it was clear where it was coming from. There was no question of Who the Provider was. When one took more than an omer, it became diminished, and if one took less than an omer, it was not deficient. The person understood that his act of gathering the manna had no connection with what he would eat. Hashem determined the amounts. Man, simply has to gather that which he was instructed to.
The Ksav Sofer explains that the Torah can only rest by one who has the mindset of a 'manna eater'. One who understands that our sustenance is like manna straight from Heaven. He stresses two ideas of what it means to be an אוֹכֵל מָן, and why this was a prerequisite to Kabbolas HaTorah.
For one who forgets Who is the source of his sustenance, falls into the trap of פֶּן תֹּאכַל וְשָׂבָעְתָּ וגו' וְשָׁכַחְתָּ אֶת ה' אֱלֹקֶיךָ וגו' וְאָמַרְתָּ בִּלְבָבֶךָ כֹּחִי וְעֹצֶם יָדִי עָשָׂה לִי אֶת הַחַיִל הַזֶּה (דברים ח יא-יד) if you will eat, and become satiated, and you will forget Hashem your G-d, and you will say in your heart "my power, and the strength of my hand have brought me this bounty". One who does not constantly remind himself that Hashem is the זָן וּמְפַרְנֵס, the One who feeds and sustains, and therefore he does not consistently thank Hashem for sustaining him, eventually forgets about his Master entirely. He does not feel beholden, and therefore he follows the dictates of his heart and not of the Torah. Remembering Who the Sustainer is, is crucial for keeping our characters suitable for learning and living according to the Torah.
Free to Learn Torah
Secondly, when Yirmihayu Hanavi gave Klal Yisrael mussar, he instructed them to engage in more Torah learning. They protested that they are occupied with sustaining their families. He countered רְאוּ דְבַר ה', see the word of Hashem. He instructed them to look, not listen. What did he show them? Many generations earlier Hashem told Moshe Rabbeinu to put away a jar of manna for safekeeping for all the following generations to see. Now Yirmiyahu showed this to the nation. Rashi says that this jar was kept as evidence that הַרְבֵּה שְׁלוּחִים יֵשׁ לוֹ לַמָּקוֹם לְהָכִין מָזוֹן לִירֵאָיו Hashem has many messengers who can prepare food for the G-d fearing. (רש"י טז לב) One does not need to toil excessively. For Hashem will send the worthy their needs with minimal exertion. Thus, in order to be able to learn Torah with equanimity one must be of the "אוֹכְלֵי הַמָּן". He needs to understand that he can increase the time spent learning, and decrease the amount of time spent working, for Hashem can provide for him regardless of the extent of his own efforts.
And to Perform the Mitzvos
Furthermore, explains the Ksav Sofer, many mitzvos in the Torah are dependent on this mindset. For example, for a farmer to let his land lie fallow on Shmitta, he needs to have a clear understanding that Hashem will send him his sustenance even without him planting the seeds. Additionally, in some generations, shmiras Shabbos involved the same understanding. One had to believe that even though he may be fired from his job as a result of keeping Shabbos, Hashem can feed him in many myriads of ways. Many other mitzvos too, including giving tzedakah, or keeping kosher, need a 'manna mindset'. Therefore, the Torah tells us; לֹא נִתְּנָה תּוֹרָה לִדְרֹשׁ אֶלָּא לְאוֹכְלֵי הַמָּן.
(כתב סופר פר' בשלח)
Not only Saying, but Living it
Saying פָּרָשַׁת הַמָּן is a well-known segulah for parnassah. The טור (סימן א) says that it is good to say it on a daily basis. The Beis Yosef explains that the reason is in order to strengthen our Emunah that parnassah is from Shamayim, and that toiling in excessive hishtadlus will not increase the output. Just like every person was allotted exactly an omer of manna, so too is every person's parnassah predetermined. Seforim Hakdoshim explain that the simple act of uttering the words of פָּרָשַׁת הַמָּן are not what serve as a segulah for parnassah. Rather thinking into them, and imbuing their meaning into our minds, is what serves as a conduit for plenty.
(טור ובית יוסף סימן א, ועוד)