As if the priests didn’t have enough on their hands- what with ensuring all of the sacrifices went smoothly, all the people were taught, and they kept themselves pure- Deuteronomy 17 assigns a new role: that of chief justice.
It’s not clear in this passage (nor in the Hebrew) if the Text here refers to this high court as consisting of one member (such as the High Priest) or a group of priests (similar to the Sanhedrin).
The reason that matters is because God has already decreed leaders of other types. Exodus 18 has men presiding over thousands, hundreds, fifties, and tens, while Numbers 11:16-17 establishes a group of seventy elders to “share the burden” with Moses.
Traditionally, this later group of seventy would morph into the Sanhedrin. That group has seventy-one members, though; Moses (or the current high priest) would be the 71st member and create the deciding vote.
That group doesn’t have any mention of priests, however, unlike the one mentioned here by Moses.
Additionally, the actual matters decided by these judges are not religious in nature. Instead, this court (or priest) judges whether or not something is murder or whether something is assault. They are things that can seem arbitrary (murder isn’t arbitrary, but there’s a difference between intentional homicide and accidental manslaughter—that’s why it can seem like a judgment call at times).
For that reason, many assume that when the person with the dispute comes to the priest for judgment, they’re actually requesting intervention from God, probably using the Urim and the Thummim. If so, then a rejection of the priest’s verdict is a rejection of God’s will, which is punishable by death.
In later years of Israel’s kingdom, a form of this was deliberately established by Jehoshaphat (2 Chronicles 19:5-11). Unfortunately, despite his efforts, it comes at a time when Judah is about to be destroyed, so you can’t really see the effects of it in the land.
So what is this court exactly?
Based on the authority that this court wields, it’s likely that Deuteronomy 17:9 lays the groundwork for what eventually would become the Great Sanhedrin—the highest judicial body in the land, centered in Jerusalem. Other courts (lesser Sanhedrins) would be developed throughout the regions, but this one reigned supreme.