And the Gadlus of a Melech is that he is thankful, like Yehuda whose very name is Hoda'ah. Singing and thankfulness (Dovid and Yehuda) are Malchus’dik, and are the opposite of complaining. And the name Rus means the mother of Dovid: שֶרִוָּהוּ (מלשון רות) לְהַקָדוֹש בָרוּךְ הוּא בְשִׁירוֹת וְתִשְבָחוֹת ברכות ז ב who satiated Hashem with song and praise – Dovid satiated with song! An extreme satisfaction. This is the key to all success, to thank and to sing.
And soon afterwards they were super successful by wiping out two powerful giants (Sichon and Og Melech HaBashan). Those who are always singing and thanking take over the world, and they are more powerful than the biggest giants. They are truly close to Hashem (Rashi). They only look upwards to Hashem. They look up at the banner of greatness, and their inborn nature to complain turns into an asset by doing Teshuva.
If You Are in Singing Mode to Hashem, You Have Everything
The Melech is anointed with Shemen HaMishcha since oil rises on top, and it is fitting that he be a: מְשׁוֹרֵר singer since song lifts you out of the foolishness of complaining, and of Kin'ah, Ta'ava, and Kavod, etc. It is interesting that Rashi in Parshas Korach when Moshe told Bnei Levi that they should be satisfied with what they have, he said: וְלַעֲמֹד לִפְנֵי הָעֵדָה טז ט Hashem has chosen you to stand before the congregation, and Rashi explains only one thing, that this means: לְשִׁיר עַל הַדוּכָן to sing on the platform. You Levi'im have the Mitzva of Shira, and if you have that then you have everything!
Singing means thankfulness and not worrying with the low-life of Kin'ah, Ta'ava, and Kavod; especially the Levi'im who sang every day a Kapit’el (chapter) from Dovid HaMelech’s Tehilim which is full of thankfulness. Moshe was telling the Levi'im that they are expected to be the opposite of being complainers. Singing means Bitachon, Hoda'ah, and Simcha; total positive!
