The above can be understood by prefacing with an explanation of the verse1 “‘G‑d is my portion,’ says my soul.”וְיוּבַן זֶה בְּהַקְדִּים מַה שֶּׁכָּתוּב "חֶלְקִי הֲוָיָ׳ אָמְרָה נַפְשִׁי",
On this verse, the Midrash comments:2וְאִיתָא בַּמִּדְרָשׁ
To illustrate with an analogy: a king entered a country accompanied by dukes, prefects, and commanders….מָשָׁל לְמֶלֶךְ שֶׁנִּכְנַס לַמְּדִינָה וְהָיוּ עִמּוֹ דֻּכָּסִין וְאִפַּרְכִּין וְאִיסְטְרָטִילוּטִין כוּ',
One person said: “I will choose a duke as my patron.” Another said: “I will choose a prefect as my patron.” And still another said: “I will choose a commander as my patron.” I.e., they wanted to attach themselves to one of the officers so that he would be their benefactor.חַד אֲמַר: אֲנָא נָסֵיב דֻּכָּסִין לְגַבַּי, חַד אֲמַר: אֲנָא נָסֵיב אִיפַּרְכִין לְגַבַּי, וְחַד אֲמַר: אֲנָא נָסֵיב אִיסְטְרָטִילוּטִין לְגַבַּי,
There was a clever person among them who said: “I will choose the king, because the others are all subject to replacement, while the king is not subject to replacement.”הָיָה פִּקֵּחַ אֶחָד לְ שָׁם, אֲמַר: אֲנָא נָסֵיב מַלְכָּא, דְּכֻלְּהוּ מִתְחַלְּפִין, וּמַלְכָּא אֵינוֹ מִתְחַלֵּף.
In the analogue, there are gentile nations who serve the sun and others who serve the moon…. Israel, by contrast, serves only the Holy One, blessed be He. This is the intent of the verse: “‘G‑d is my portion,’ says my soul.”כֵּן אֻמּוֹת הָעוֹלָם מֵהֶן עוֹבְדִין לַחַמָּה וּמֵהֶן עוֹבְדִין לַלְּבָנָה כוּ' אֲבָל יִשְׂרָאֵל אֵינָן עוֹבְדִין אֶלָּא לְהַקָּדוֹשׁ בָּרוּךְ הוּא, הָדָא הוּא דִּכְתִיב: "חֶלְקִי הֲוָיָ׳ אָמְרָה נַפְשִׁי".
There are well-known explanations regarding the details of the Midrash.3וְיָדוּעַ הַדִּיּוּק בָּזֶה,
For, on the surface, its intent requires explanation:דְּלִכְאוֹרָה,
Everyone, even one who is not clever, even a very young child,4הֲרֵי גַּם מִי שֶׁאֵינוֹ פִּקֵּחַ וַאֲפִלּוּ תִּינוֹק קָטָן
knows that the king is greater than the duke or the other officers.יוֹדֵעַ שֶׁהַמֶּלֶךְ הוּא גָּדוֹל יוֹתֵר מֵהַדֻּכָּסִין וְכוּ',
Why then would “cleverness” be required to choose the king?וּמַה צְרִיכִים לְפִקְחוּת בִּכְדֵי לִבְחֹר בְּהַמֶּלֶךְ.
Also, the rationale given for choosing the king requires explanation.וְגַם,
Even if the position of the duke and the other officers would be permanent and they would not be subject to replacement, it is obvious that the king is greater than they.הֲרֵי גַּם אִם הַדֻּכָּסִין וְכוּ' לֹא הָיוּ מִתְחַלְּפִין, הָיָה מוּבָן בְּפַשְׁטוּת שֶׁהַמֶּלֶךְ הוּא גָּדוֹל מֵהֶם
[This is certainly true according to the well-known explanation5 of the verse:6 “From his shoulders up, he was taller than all the people.”[וּבִפְרָט לְפִי הַיָּדוּעַ בְּפֵרוּשׁ הַכָּתוּב "מִשִּׁכְמוֹ וָמַעְלָה גָּבֹהַּ מִכָּל הָעָם",
The verse refers to King Shaul, the first of Israel’s kings. The spiritual implications, however, apply to all proper monarchs. They possess inner qualities that are inherently loftier than those of their subjects.
Implied is that the king’s shoulders, i.e., his emotions that are drawn down from the intellect in his head and which influence his lower levels, are higher than the heads (i.e., the intellect) of the people at large.שֶׁגַּם שִׁכְמוֹ שֶׁל הַמֶּלֶךְ, הַיְינוּ הַמִּדּוֹת שֶׁנִּמְשָׁכִים מֵהַשֵּׂכֶל שֶׁבָּרֹאשׁ וּלְמַטָּה מִמֶּנּוּ, הוּא גָּבֹהַּ יוֹתֵר מֵהָרֹאשׁ (הַשֵּׂכֶל) שֶׁל כָּל הָעָם,
The king’s inherent superiority places him in a different category than the entire nation.
This includes even the nation’s most elevated officers, including the dukes, prefects, and commanders.]שֶׁבָּזֶה (כָּל הָעָם) נִכְלָלִים גַּם הַשָּׂרִים הֲכִי גְּדוֹלִים],
Why then is it necessary to state the rationale that all the officers “are subject to replacement”?7וְלָמָּה צָרִיךְ לְהַטַּעַם דְּכֻלְּהוּ מִתְחַלְּפִין.
Seemingly, the king should be chosen in any case because of his superior qualities.

Summary

On the verse, “‘G‑d is my portion,’ says my soul,” the Midrash offers an analogy:
A king entered a country accompanied by dukes, prefects, and commanders…. One person said: “I will choose a duke as my patron.” Another said: “I will choose a prefect as my patron.” And still another said: “I will choose a commander as my patron.” There was a clever person among them who said: “I will choose the king, because the others are all subject to replacement, while the king is not subject to replacement.”
In the analogue, there are gentile nations who serve the sun and others who serve the moon…. Israel, by contrast, serves only the Holy One, blessed be He. This is the intent of the verse: “‘G‑d is my portion,’ says my soul.”
The Midrash provokes questions:
a) Why must one be “clever” to choose the king? Seemingly, choosing him should be obvious.
b) The rationale given for choosing the king – because all the officers “are subject to replacement” – requires explanation. Shouldn’t the king be chosen in any case because of his superior qualities?