In Focus: Let’s put Deuteronomy 17:12 in focus. There are three necessary parts in this one verse.
In Nerdiness: The passages on the kingdom come into view here. Was Moses foreseeing a time when they would want a king? Or is this evidence that Deuteronomy was composed later? How you answer that is more a function of your presuppositions about Scripture than your Old Testament skills. I say that God inspired Moses looking forward, because my presupposition is that God is able to do so. Others take a different view. Passages like this test those assumptions.