Here Moses passes from the judges to the people at large; from charging officials to judge righteously, to reminding the people that they also had received from him commandments which they had to obey.
The "things" referred to are either the injunctions specified in Exodus 21:1-36; etc; or simply the instructions mentioned in the preceding verses. God had called the Israelites out of Egypt that they should go up at once to Canaan, and he had by Moses done all that was needed for this.
But they had been rebellious, and had opposed God's commands, the consequence of which was that they had been made to experience various trials, especially to wander nearly forty years in the wilderness, so that of those who came out of Egypt only two were privileged to see the Promised Land.
The words of Moses in this section supplement and complete the narrative in Numbers 13:1-33.; but the words are those, not of a compiler, but of one who had been himself a witness of all he narrates.