He was king - i. e., not Moses but the Lord became king.

And he was king in Jeshurun,.... That is, in Israel, or over the people of Israel, of which name of theirs; see Gill on Deuteronomy 32:15; either God, as Jarchi; for the government of the Israelites was a theocracy, and their laws were immediately from God, and by him they were guided and directed in all things; wherefore, when they were so importunate for a change in their government, and to have a king over them, they are said to reject the Lord, that he should not reign over them, 1 Samuel 8:7; or Moses, as Aben Ezra on the place, Maimonides (f), and others (g); who, under God, had the civil government of the Hebrews; both may be received, God was the supreme Governor, and Moses the chief magistrate under him:

when the heads of Israel and the tribes of the people were gathered together; at Mount Sinai, to hear the law there and then given, or to hear it repeated by Moses, as in this book of Deuteronomy, who were at different times convened together for that purpose, see Deuteronomy 1:1; next follow the particular blessings of the several tribes, beginning with Reuben the firstborn.

(f) In Misn. Shebuot, c. 2. sect. 2.((g) Philo de Vita Mosis, l. 3. p. 681.

And he was king in Jeshurun, when the heads of the people and the tribes of Israel were gathered together.

33:5 He was king in Jeshurun - Moses was their king not in title, but in reality, being under God, their supreme governor, and law giver. Gathered together - When the princes and people met together for the management of public affairs, Moses was owned by them as their king and lawgiver.

33:1-5 To all his precepts, warnings, and prophecies, Moses added a solemn blessing. He begins with a description of the glorious appearances of God, in giving the law. His law works like fire. If received, it is melting, warming, purifying, and burns up the dross of corruption; if rejected, it hardens, sears, pains, and destroys. The Holy Spirit came down in cloven tongues, as of fire; for the gospel also is a fiery law. The law of God written in the heart, is a certain proof of the love of God shed abroad there: we must reckon His law one of the gifts of his grace.