Deuteronomy 17 - The sacrifices and offerings brought to the Lord must be as perfect as possible. God deserves nothing less. Those who practice idolatry are to be severely judged by stoning for they not only have turned away from the Lord but have led others to do so as well. Israelites were to obey God-appointed officials who oversee the nation. Please note the end of this chapter as Moses gives instructions how to select a king and what his responsibilities are.
Deuteronomy 18 - The Levites are to be always cared for. There is to be no practice of divination, fortune telling, or any related activity. God will send a Prophet one day who will be greater than all others. Christ Jesus is this Prophet. The chapter ends with clear evidence when someone is a false prophet: what they predict doesn't come to pass.
Deuteronomy 19 - Moses explains again the need for Cities of Refuge. He stresses judgment is to be passed on someone who tried to get someone else in trouble. If a person maliciously lied against another person in order to get them into trouble and be punished, the same punishment was to be directed against the false accuser.
Deuteronomy 20 - God knew the inevitable of facing warfare would happen to the Jewish people. God placed certain procedures to be followed in facing an enemy. However, the Lord made clear that when the Israelites were facing those in Canaan, there was to be no leniency in softening judgment against them. They were to be eradicated from the land.