When you enter the land the LORD your God is giving you and have taken possession of it and settled in it, and you say, “Let us set a king over us like all the nations around us,” be sure to appoint over you a king the LORD your God chooses. He must be from among your fellow Israelites. Do not place a foreigner over you, one who is not an Israelite.
YHWH did not intend to give the Jewish people a king at that time nor any other kind of mediator between Him and them. However, seeing the weakness of the people and their tendency to always want to follow the customs of the pagans, he consents to this intention insofar as the king is a Jew who respects the Commandments.
Our situation is exactly the same. The weak and rebellious nature of man makes it impossible to keep the law. We therefore need an intercessor who is perfect and without sin, that is to say, capable of obeying the commandments of YHWH unconditionally.
Only a King who is none other than the very Word of Elohim is able to save humanity from the judgment of YHWH.
This Word who became flesh and who appeared among us in the person of Jesus of Nazareth.
Therefore, our Father has given us a one and eternal Kingdom through his Son. In Christ we have an eternal King, who is the Son of our Father. Therefore, Jesus is the one and only person who perfectly embodies and fulfills this commandment we just read.
From here on, we are forbidden to accept or keep any other kings and alien rules.
See also Laws for the King: Commandments Concerning the King: Horses and Wives