כִּ֤י מֶ֖לֶךְ כָּל־הָאָ֥רֶץ אֱלֹהִ֗ים זַמְּר֥וּ מַשְׂכִּֽיל׃
Car Dieu est roi de toute la terre: entonnez un solennel cantique.
Rabbeinu Bahya
A Midrashic approach (Pessikta Zutrata): The “king” referred to in the line ויהי בישורון מלך, is Moses, seeing that people had heard the entire Torah (legislation) from his mouth. The Torah means that the manner in which all the people including their tribal heads assembled around him, gave Moses the stature of king. This was not the first time that Moses had acted as lawgiver. It had occurred in Deut. 31,9 already when he had given the Torah to the priests, the Levites, carriers of the Holy Ark. We also find Moses ordering all the people to appear in his presence in Deut. 31,28.
Another way of understanding our verse is that the “king” described here is G’d Himself. The Torah describes that G’d became king only when all the tribal heads assembled. We find something similar described in Psalms 47,8-10 where David refers to G’d’s position as “king” in connection with the leaders of mankind indicating that they accept Him as such. In the case of the Jewish people: “when the leaders of the people volunteered to rally around Him.” We have another similar description of G’d becoming king in Amos 9,6. [The prophet portrays that G’d cannot build His chambers in heaven until an assembly of His loyal people have laid the foundation for this on earth. Ed.] The common denominator in all these verses is that G’d does not impose Himself as “king,” but waits until His creatures manifest their desire for Him to be their king.
Another way of understanding our verse is that the “king” described here is G’d Himself. The Torah describes that G’d became king only when all the tribal heads assembled. We find something similar described in Psalms 47,8-10 where David refers to G’d’s position as “king” in connection with the leaders of mankind indicating that they accept Him as such. In the case of the Jewish people: “when the leaders of the people volunteered to rally around Him.” We have another similar description of G’d becoming king in Amos 9,6. [The prophet portrays that G’d cannot build His chambers in heaven until an assembly of His loyal people have laid the foundation for this on earth. Ed.] The common denominator in all these verses is that G’d does not impose Himself as “king,” but waits until His creatures manifest their desire for Him to be their king.