Deutéronome 33:5

And he was king in Israel: when the chiefs of the people were gathered together, the tribes of Israel were obedient to him.

king This denotes Moshe, from whose mouth the heads of the nation heard the Torah elucidated [the halakha [Rosh HaShana 32b] is that this verse may be used in the liturgy to refer to God’s majesty — Translator]. The intent of the verse is that Moshe was like a king, who gathered before him the chiefs of the tribes. This explanation is substantiated by the verses which state that the Torah was given to the kohanim [31: 9] (who — in my opinion — are meant by “all His holy ones are in Your hand” [: 3]), and then to all the elders of Israel [31: 9] (they being meant by when the chiefs of the people assembled). In fact, in the above-cited passage, Scripture states, “Assemble to me all the elders of your tribes” [31: 28]. However, Rabbi Y e hudah HaLevy, of blessed memory, said that the king was allegorical of the Torah. He also gave a similar explanation to “There was no king in Israel” [Judges 18: 1].

AND THERE WAS A KING IN JESHURUN. This alludes to the aforementioned Name [in Verse 2: ‘The Eternal’ came from Sinai], Who was King over Israel when they were upright and all the heads of the people and all tribes of Israel were gathered together. Now this verse, too, is connected [with the above theme — the Revelation at Sinai], and the sense thereof is that Israel will always say: “The Torah which Moses commanded us will forever be an inheritance to the entire congregation of Jacob. We shall never alter it or change it.” And they will further say that “G-d became King over Israel when our leaders, our elders, our judges and all tribes of Israel gathered, for we all, together, accepted His reign upon ourselves for all generations, and we are obligated to keep His Law and [acknowledge] His Kingdom forever.” This commandment is the precept of I am the Eternal thy G-d, and it constitutes “the acknowledgment of the Kingdom of Heaven,” as I have explained there. Thus he mentioned the Torah in general, and the Kingdom of Heaven in partizcular, for whoever acknowledges the Kingdom of Heaven denies the idols and acknowledges the entire Torah. 6. The people thus intimated that they and their leaders accepted [the commandment to acknowledge] the Kingdom of Heaven [directly] from the mouth of the Almighty and saw that He is King of Israel and his Redeemer. They accepted the Torah from the mouth of Moses for they took upon them, and upon their seed to believe in him and to do whatever he commands in behalf of the King, just as they said [to Moses], and thou shalt speak unto us all that the Eternal our G-d may speak unto thee, and we will hear it, and do it.
This interpretation of the verse is clear and well founded. It accords with the rendering of the Rabbis in the Gemara of Tractate Rosh Hashanah:. Now, each unit of ten verses is composed of three verses from the Pentateuch, three from the Prophets, three from the Writings, with one concluding verse from the Pentateuch. On these four verses from the Pentateuch concerning the Sovereignty of G-d the Rabbis in the Gemara asked: “But only three verses referring to Sovereignty etc.” “But only three verses referring to Sovereignty [of G-d] are found [in the Five Books of Moses]! The Eternal shall reign for ever and ever; The Eternal his G-d is with him, and the ‘t’ruah’ (shouting) for the King is among them; And there was a King in Jeshurun.” …

ויהי בישורון מלך, since that occasion G’d became “King” in Israel among all those who study Torah more than superficially.

בהתאסף ראשי עם, at the time of the giving of the Torah, when, according to Deut. 5,19, all the elders and leaders of the people are described as approaching Moses, telling him (verse 20) that G’d had shown them His glory,

יחד שבטי ישראל, G’d had thus become King over all the tribes of Israel at one and the same time as they all accepted His status as being their supreme authority. The words which the people used to express this acceptance were:ואת תדבר אלינו את כל אשר ידבר ה' אלוקינו אליך ושמענו ועשינו, “and you say to us all that the Lord our G’d will say to you, and we will hear it and do it.” (Deut.5,24)

ויהי בישורון מלך בהתאסף ראשי עם, “and there was a king in Jeshurun when the heads of the people were gathered.” When the Jewish people are truly united and relate to one another as true brothers, then G–d is truly King over them. When they quarrel among themselves then G–d cannot truly be seen as being their King.