Ramban explains that the daily manna was meant to test whether Israel would follow God’s instructions exactly and to habituate them to trust that He would provide anew each day.
לְמַעַן אֲנַסֶּנּוּ הֲיֵלֵךְ בְּתוֹרָתִי אִם יִשְׁמְרוּ מִצְוֹת הַתְּלוּיוֹת בּוֹ שֶׁלֹּא יוֹתִירוּ מִמֶּנּוּ וְלֹא יֵצְאוּ בְּשַׁבָּת לִלְקֹט. לְשׁוֹן רַשִׁ"י (רש"י על שמות ט"ז:ד'). וְאֵינֶנּוּ נָכוֹן, אֲבָל הוּא כְּמוֹ שֶׁאָמַר (שם טז) "הַמַּאֲכִלְךָ מָן בַּמִּדְבָּר אֲשֶׁר לֹא יָדְעוּן אֲבֹתֶיךָ לְמַעַן עַנֹּתְךָ וּלְמַעַן נַסֹּתֶךָ לְהֵטִיבְךָ בְּאַחֲרִיתֶךָ", כִּי נִסָּיוֹן הוּא לָהֶם שֶׁלֹּא הָיָה בְּיָדָם מָזוֹן, וְלֹא יִרְאוּ לָהֶם עֵצָה בַּמִּדְבָּר רַק הַמָּן, שֶׁלֹּא יָדְעוּ מִתְּחִלָּה, וְלֹא שָׁמְעוּ מֵאֲבוֹתָם, וְיוֹרֵד לָהֶם דְּבַר יוֹם בְּיוֹמוֹ וְיִרְעֲבוּ אֵלָיו, וְעִם כָּל זֶה שָׁמְעוּ לָלֶכֶת אַחֲרֵי הַשֵּׁם לֹא בַּמִּדְבָּר לֹא מְקוֹם לֶחֶם: וְכָכָה אָמַר לָהֶם עוֹד (שם ח ב) "וְזָכַרְתָּ אֶת כָּל הַדֶּרֶךְ אֲשֶׁר הֹלִיכֲךָ ה' אֱלֹהֶיךָ זֶה אַרְבָּעִים שָׁנָה בַּמִּדְבָּר לְמַעַן עַנֹּתְךָ וּלְמַעַן נַסֹּתֶךָ לָדַעַת אֶת אֲשֶׁר בִּלְבָבְךָ הֲתִשְׁמֹר מִצְוֹתָיו אִם לֹא", כִּי הָיָה יָכוֹל לְהוֹלִיכָם בְּדֶרֶךְ הֶעָרִים אֲשֶׁר סְבִיבוֹתֵיהֶם, וְהוֹלִיכָם בְּמִדְבַּר נָחָשׁ שָׂרָף וְעַקְרָב (שם טו), וְשֶׁלֹּא יִהְיֶה לָהֶם לֶחֶם רַק מִן הַשָּׁמַיִם דְּבַר יוֹם בְּיוֹמוֹ, לְנַסּוֹתָם וּלְהֵטִיב לָהֶם בָּאַחֲרוֹנָה, שֶׁיַּאֲמִינוּ בּוֹ לְעוֹלָם. וּכְבָר פֵּרַשְׁתִּי עִנְיַן הַנִּסָּיוֹן בְּפָסוּק "וְהָאֱלֹהִים נִסָּה אֶת אַבְרָהָם" (בראשית כב א). וְהָרַב אָמַר בְּמוֹרֶה הַנְּבֻכִים (ג כד) לָדַעַת כָּל יוֹדֵעַ וּלְנַסּוֹת הֲיֵשׁ תּוֹעֶלֶת בַּעֲבוֹדַת הָאֵל, וְאִם יֵשׁ בָּהּ סִפּוּק צֹרֶךְ אִם לֹא. וְאִם כֵּן הָיָה רָאוּי שֶׁיֹּאמַר "לְמַעַן יְנַסֶּה לָדַעַת": וְהִנֵּה לֹא הִזְכִּיר כָּאן דָּבָר רַק הַמָּן שֶׁהוּא הַלֶּחֶם שֶׁהִמְטִיר לָהֶם, אֲבָל כַּאֲשֶׁר אָמַר לָהֶם מֹשֶׁה (שמות ט"ז:ח') בְּתֵת ה' לָכֶם בָּעֶרֶב בָּשָׂר לֶאֱכֹל וְלֶחֶם בַּבֹּקֶר לִשְׂבֹּעַ, יָדַעְנוּ כִּי הַכֹּל נֶאֱמַר לוֹ, אֲבָל הַכָּתוּב יְקַצֵּר בַּדְּבָרִים הַנִּכְפָּלִים בְּעִנְיַן הַצִּוּוּי אוֹ בַּסִּפּוּר, כַּאֲשֶׁר הִזְכַּרְתִּי לְךָ פְּעָמִים רַבִּים (לעיל ט יב, י יב, יא א), וּפְעָמִים לֹא יַזְכִּיר הָאֶחָד כְּלָל, דִּכְתִיב בַּפָּרָשָׁה הַזֹּאת (שמות ט"ז:ל"ב) זֶה הַדָּבָר אֲשֶׁר צִוָּה ה' מְלֹא הָעֹמֶר מִמֶּנּוּ, וְלֹא נִכְתְּבָה הַצַּוָּאָה כְּלָל, וְכֵן בִּמְקוֹמוֹת רַבִּים: וְעַל דַּעַת הָאוֹמְרִים (הראב"ע) כִּי "לֶחֶם" - כָּל מַאֲכָל, יִתָּכֵן שֶׁיֹּאמַר הִנְנִי מַמְטִיר לָכֶם לֶחֶם עַל הַמָּן וְעַל הַשְּׂלָו, כִּי יִתֵּן לָהֶם שְׁאֵלָתָם שֶׁשָּׁאֲלוּ לֶחֶם וּבָשָׂר, וּמֹשֶׁה פֵּרֵשׁ שֶׁיִּהְיֶה הַבָּשָׂר בָּעֶרֶב לֶאֱכֹל וְהַלֶּחֶם בַּבֹּקֶר לִשְׂבֹּעַ כְּדֶרֶךְ כָּל הָאָרֶץ:
THAT I MAY TRY THEM, WHETHER THEY WILL WALK IN MY LAW OR NOT. “I.e., whether they will observe the commandments associated with it, such as [the laws] that they should not leave [a remainder] of it until the morning and that they should not go out on the Sabbath to collect it.” Thus the language of Rashi. But this is not correct. Rather, the intent [of the trial mentioned here] is as He said, Who fed thee in the wilderness with manna, which thy fathers knew not; that He might afflict thee, and that He might try thee, to do thee good at thy latter end. [The manna itself] was a trial to them, since they had no food in the wilderness and were without recourse to any sustenance except the manna, which they knew not from before and had never heard of from their fathers. Each day’s quantity came down on its day, and they were eagerly desirous for it. Yet with all this, they hearkened to walk after G-d to a place of no food. And so indeed He said to them again, And thou shalt remember all the way in which the Eternal thy G-d hath led thee these forty years in the wilderness, that He might afflict thee, to try thee, to know what was in thy heart, whether thou wouldest keep His commandments, or no. He could have led them by way of the cities that were round about them. Instead, He led them through the wilderness wherein were serpents, fiery serpents, and scorpions, and each day’s quantity of food would come to them only from heaven in order to try them and to do them good at the end so that they would believe in Him forever. I have already explained the matter of “trial” in the commentary on the verse, And G-d tried Abraham. The Rabbi [Moshe ben Maimon] has written in the Moreh Nebuchim [on the verse before us, That I may try them, whether they will walk in My law or not, that it means] that “everyone capable of knowledge should know and determine whether there is usefulness in the service of G-d, and whether there is adequate satisfaction in it or not.” But if so, it would have been proper for Him to say, “that He may try them to know!” Now Scripture mentions here only the matter of manna, which was “the bread” which He caused to rain upon them, [and it does not refer to the flesh which He gave them]. However, from that which Moses told them, This shall be, when the Eternal shall give you in the evening flesh to eat, and in the morning bread to the full, we know that everything was told to him. It is only that when a subject is mentioned twice, Scripture shortens it in the report of the command or the narrative, as I have mentioned to you many times. At times, it omits one — [the command or the narrative] — altogether, such a case being the verse written in this section: This is the thing which the Eternal hath commanded: Let an omerful of it [the manna] be kept throughout your generations, and the command [of G-d to Moses] is not recorded at all. This is also the case in many places. But in the opinion of those scholars who say that lechem here means “all food,” it is possible that by saying, Behold, I will cause to rain ‘lechem,’ the meaning refers to both the manna and to the quail, i.e., that He would fulfill their request for bread and flesh. Moses explained that the flesh would be [available] to eat in the evening, and the bread would be [available] in the morning to the full, as is the customary way.
