The Chinukh explains the mitzvah of birkat hamazon and its underlying idea: to remember God's kindness and train the soul in gratitude. It presents blessings as a pedagogic act that shapes inner consciousness.
מִשָּׁרְשֵׁי הַמִּצְוָה. הַקְדָּמָה, הֲלֹא הִגַּדְתִּי לְךָ בְּנִי בְּמָה שֶׁקָּדַם, כִּי לַשֵּׁם בָּרוּךְ הוּא כָּל הַכָּבוֹד וְהַהוֹד וְכָל הַטּוֹב וְכָל הַחָכְמָה וְכָל הַיְּכֹלֶת וְכָל הַבְּרָכָה, וְדִבְרֵי בֶּן אָדָם וְכָל מַעֲשֵׂהוּ אִם טוֹב וְאִם רָע לֹא יוֹסִיף וְלֹא יִגְרַע, עַל כֵּן צָרִיךְ אַתָּה לְהַבְחִין כִּי בְּאָמְרֵנוּ תָּמִיד בַּבְּרָכוֹת בָּרוּךְ אַתָּה הַשֵּׁם אוֹ יִתְבָּרַךְ, אֵין הַמַּשְׁמָעוּת לְפִי הַדּוֹמֶה, לְהוֹסִיף בְּרָכָה בְּמִי שֶׁאֵינֶנּוּ צָרִיךְ לְשׁוּם תּוֹסֶפֶת חָלִילָה, כִּי הוּא הָאָדוֹן עַל הַכֹּל וְעַל הַבְּרָכוֹת, הוּא מְחַדֵּשׁ אוֹתָן, וּמַמְצִיאָן מֵאַיִן, וּמַשְׁפִּיעַ מֵהֶן שֶׁפַע רַב בַּאֲשֶׁר יִהְיֶה שָׁם רְצוֹנוֹ הַטּוֹב. עַל כֵּן צְרִיכִין אָנוּ לְחַפֵּשׂ כַּוָּנַת הָעִנְיָן מַהוּ, וְלֹא נוֹצִיא זְמַנֵּנוּ בַּמֶּה שֶׁהָעֵסֶק בּוֹ תָּמִיד מִבְּלִי הֲבָנָה בּוֹ כְּלָל. וַאֲנִי הַמְּעוֹרֵר, אֵין מַחֲשַׁבְתִּי שֶׁיַּשִּׂיג שִׂכְלִי אֲפִלּוּ כְּטִפָּה מִן הַיָּם בַּאֲמִתַּת הָעִנְיָן, כִּי כְּבָר הֻגַּד לִי וְשָׁמַעְתִּי מִפִּי חֲכָמִים, כִּי יֵשׁ בִּדְבָרִים אֵלֶּה, יְסוֹדוֹת חֲזָקִים וְסוֹדוֹת נִפְלָאִים, יוֹדִיעוּם חַכְמֵי הַתּוֹרָה לְתַלְמִידֵיהֶם כְּשֶׁהֵם נְבוֹנִים וּכְשֵׁרִים וּבְכָל מַעֲשֵׂיהֶם נָאִים, אֲבָל רַב חֶפְצִי לְהַשִּׂיג בָּזֶה קְצָת טַעַם יַשִּׁיאֵנִי לְדַבֵּר בּוֹ, וְאוּלַי הָיְתָה טוֹבָה הַשְּׁתִיקָה, אֲבָל הָאַהֲבָה תְּקַלְקֵל הַשּׁוּרָה. יָדוּעַ הַדָּבָר וּמְפֻרְסָם, כִּי הַשֵּׁם בָּרוּךְ הוּא, פּוֹעֵל כָּל הַנִּמְצָא וּבָרָא הָאָדָם וְהִשְׁלִיטוֹ עַל הָאָרֶץ וְעַל כָּל אֲשֶׁר בָּהּ, וּמִמִּדּוֹתָיו בָּרוּךְ הוּא, שֶׁהוּא רַב חֶסֶד וְהוּא חָפֵץ בְּטוֹבַת בְּרִיּוֹתָיו, וְרוֹצֶה לִהְיוֹתָן רְאוּיִין וְזַכָּאִין לְקַבֵּל טוֹבָה מֵאִתּוֹ, וְזֶה בֶּאֱמֶת מִשְּׁלֵמוּתוֹ בָּרוּךְ הוּא, כִּי לֹא יִקָּרֵא שָׁלֵם בְּטוֹבָה, רַק מִי שֶׁהוּא מֵיטִיב לַאֲחֵרִים זוּלָתוֹ, אֵין סָפֵק בָּזֶה לְכָל בֶּן דַּעַת. וְאַחַר הַסְכָּמָה זוֹ שֶׁיָּדַעְנוּ בְּחִיּוּב מֵרֹב שְׁלֵמוּת טוּבוֹ שֶׁחֶפְצוֹ לְהָרִיק עָלֵינוּ מִבִּרְכָתוֹ, נֹאמַר שֶׁעִנְיַן הַבְּרָכָה שֶׁאָנוּ אוֹמְרִים לְפָנָיו אֵינֶנּוּ, רַק הַזְכָּרָה לְעוֹרֵר נַפְשֵׁנוּ בְּדִבְרֵי פִּינוּ כִּי הוּא הַמְבֹרָךְ, וּמְבֹרָךְ יִכְלֹל כָּל הַטּוֹבוֹת, וּמִתּוֹךְ הַהִתְעוֹרְרוּת הַטּוֹב הַזֶּה בְּנַפְשֵׁנוּ וְיִחוּד מַחְשַׁבְתֵּנוּ לְהוֹדוֹת אֵלָיו שֶׁכָּל הַטּוֹבוֹת כְּלוּלוֹת בּוֹ וְהוּא הַמֶּלֶךְ עֲלֵיהֶם לְשַׁלְּחָם עַל כָּל אֲשֶׁר יַחְפֹּץ, אָנוּ זוֹכִים בַּמַּעֲשֶׂה הַטּוֹב הַזֶּה לְהַמְשִׁיךְ עָלֵינוּ מִבִּרְכוֹתָיו, וְאַחַר הַזְכָּרָה וְהוֹדָאָה זוֹ לְפָנָיו, אָנוּ מְבַקְשִׁים מִמֶּנּוּ מַה שֶׁאָנוּ צְרִיכִים דַּעַת, אוֹ סְלִיחָה לַעֲוֹנֹתֵינוּ, אוֹ רְפוּאָה, אוֹ עֹשֶׁר וְכָל דָּבָר. וְכֵן אַחַר הַבַּקָּשָׁה מִמֶּנּוּ, אָנוּ חוֹזְרִין וּמוֹדִים אֵלָיו בָּזֶה לוֹמַר, כִּי מִמֶּנּוּ יָבוֹא אֵלֵינוּ, וְזֶהוּ פְּתִיחָה וַחֲתִימָה שֶׁל הַבְּרָכוֹת, פֶּן נֵחָשֵׁב כְּעֶבֶד שֶׁנָּטַל פְּרָס מֵרַבּוֹ וְהוֹלֵךְ לוֹ בְּלֹא רְשׁוּת כְּמִתְגַּנֵּב. וְנִמְצָא לְפִי הַנָּחַת טַעַם זֶה, שֶׁיִּהְיֶה בָּרוּךְ תֹּאַר, כְּלוֹמַר, הוֹדָאָה עָלָיו כִּי הוּא כּוֹלֵל כָּל הַבְּרָכוֹת. וּבִלְשׁוֹן יִתְבָּרַךְ שֶׁאָנוּ מַזְכִּירִין תָּמִיד שֶׁהוּא מֵהִתְפַּעֵל נֶאֱמַר, שֶׁהַכַּוָּנָה בּוֹ שֶׁאֲנַחְנוּ מִתְחַנְּנִים אֵלָיו שֶׁיִּהְיֶה רָצוֹן מִלְּפָנָיו לְסַבֵּב לֵב בְּרִיּוֹתָיו לִהְיוֹת נָכוֹן לְפָנָיו שֶׁיּוֹדוּ הַכֹּל אֵלָיו וּבוֹ יִתְהַלְּלוּ, וְזֶהוּ פֵּרוּשׁ יִתְבָּרַךְ כְּלוֹמַר, יְהִי רָצוֹן מִלְּפָנֶיךָ שֶׁכָּל בְּנֵי הָעוֹלָם יִהְיוּ מְיַחֲסִים הַבְּרָכָה אֵלֶיךָ, וּמוֹדִים כִּי מִמְּךָ תִּתְפַּשֵּׁט בַּכֹּל, וְעִם הוֹדָאַת הַכֹּל בָּזֶה תָּנוּחַ בִּרְכָתוֹ בָּעוֹלָם, וְיִשְׁלַם חֶפְצוֹ, שֶׁהוּא חָפֵץ לְהֵטִיב, כְּמוֹ שֶׁאָמַרְנוּ, וְתַשְׁלוּם הַחֵפֶץ תַּכְלִית כָּל הַמְבֻקָּשׁ. וְהִנֵּה מָצָאנוּ קְצָת טַעַם אַף בִּלְשׁוֹן יִתְבָּרַךְ הַמַּתְמִיהַּ. וּמִן הַפֵּרוּשׁ (נ"א הַשֹּׁרֶשׁ) הַזֶּה, מָה שֶׁאָמְרוּ זִכְרוֹנָם לִבְרָכָה (חולין ס ב) שֶׁהַקָּדוֹשׁ בָּרוּךְ הוּא מִתְאַוֶּה לִתְפִלָּתָן שֶׁל צַדִּיקִים, לוֹמַר, שֶׁחֶפְצוֹ שֶׁיַּעֲשׂוּ פְּעֻלָּה שֶׁיִּזְכּוּ בָּהּ לְפָנָיו וְיַמְשִׁיכוּ עֲלֵיהֶם מִטּוּבוֹ, כִּי חָפֵץ לַעֲשׂוֹת חֶסֶד הוּא, וְלָתֵת עֲלֵיהֶם מִבִּרְכָתוֹ מִטּוּב שְׁלֵמוּתוֹ כְּמוֹ שֶׁכָּתוּב, וְזֶהוּ הַשֹּׁרֶשׁ הַגָּדוֹל לְכָל אֲשֶׁר יַעֲשֶׂה הָאָדָם טוֹב בָּעוֹלָם הַזֶּה, שֶׁזֶּה שְׂכָרוֹ מֵאֵת הַשֵּׁם שֶׁמַּשְׁלִים חֶפְצוֹ, בַּאֲשֶׁר הוּא רוֹצֶה בְּטוֹבָתָן שֶׁל בְּרִיּוֹת.
From the roots of the commandment, [there is a need to] preface that, have I not told you my son, in what has preceded, that all glory, all majesty, all the good, all wisdom, all power and blessing are of God, blessed be He. And the words of people and all of their deeds — whether good or bad — will not add or subtract [from Him]. Hence you must distinguish that in our always saying in the blessings, “Blessed are You, God,” or [in our saying,] “May He be blessed,” the understanding is not as it seems, to add blessing to the One Who does need any addition, God forbid. As He is the Master over everything and over all the blessing; He renews them and creates them and emanates great abundance from them when His good will is [present] there. Therefore, we must search what is the intention of the matter and not expend our time in that with which we are always involved without any understanding at all. And it is not my thought — I, the one that raises [it] — that my intellect will grasp even like a drop in the ocean of the truth of the matter. As it has already been told to me and I heard from the mouth of sages that there is in these things strong foundations and wonderful secrets — the Torah sages inform their students [of them] when they are understanding and proper and all of their actions are pleasant. But my great will to grasp a little of the reason in this impels me to speak about it. And maybe silence would have been better, but “love spoils [sense of what is proper].” The matter is known and famous that God, may He be blessed, moves all that exists and created man and put him in control over the earth and over every thing that is in it. And it is from His traits, blessed be He, that He is of much kindness and that He desires the good of His creatures, and [so] He wants them to be fitting and meriting to receive goodness from Him. And this is really from His perfection, may He be blessed. As only one who gives to others besides himself can be called perfect in the good — there is no doubt about this to any intelligent person. And since [we are in] agreement [about] this, that we know that it is obligatory from the perfection of His goodness, that His desire is to pour down His blessing upon us, we shall say that the matter of the blessing that we say in front of Him is only a mention to arouse ourselves through the words of our mouths that He is the blessed One, and the blessed One that contains all of the goodnesses. And through this good arousal of ourselves and the designation of our thoughts to admit to Him that all of the goodnesses are included in Him and He is the King over them, to send them to all that He desires, we merit through this good action to bring from His blessings upon us. And after this mention and this admission in front of Him, we request from Him that which we need [of] knowledge, or the pardon of our iniquities, or healing, or wealth or anything. And so [too,] after the request from Him, we repeat and admit to Him about this, to say that it comes to us from Him. And this is the opening and the conclusion of the blessings. [The reason for the latter is that we not] be considered like a slave who took a reward from his master and goes away without permission, like a thief. And it comes out according to the premise [created by] this reason that “blessed” is an adjective, meaning to say it is an admission to Him that He contains all of the blessings. And [about] the expression, “may He be blessed,” that we always mention — which is [in] the reflexive case — we can say that the intention of it is that we are supplicating to Him that it be His will in front of Him to cause the hearts of His creatures to be prepared in front of Him that all should admit to Him and praise Him. And this is the explanation of “may He be blessed,” meaning to say, “It should be Your will in front of You, that all people of the world will relate all blessing to You and admit that everything in the world emanates from You,” and that His will be completed — as He wants to do good, as we have said. And the fulfillment of the Will is the purpose of all that ask. And behold, we have found an explanation even for the puzzling expression of “may He be blessed.” And from this understanding (other versions: root), that which they, may their memory be blessed, said (Chullin 60b) that the Holy One, blessed be He, craves the prayers of the righteous [is] to say that His desire is that they do an act through which they will merit in front of Him and bring down from His goodness upon them; as He is One Who desires to do kindness and to give from His blessing upon them, from the good of His perfection, as is written. And this is the great root to all the good that a man does in this world — that his reward from God [is because] he fulfills His desire, in that He wants the good of the creatures.