Now about what he commanded them to teach. After His resurrection, before He ascended, Jesus had just spent forty days under the new covenant teaching the Disciples. It is these teachings that He was referring to. These were the teachings of the new covenant. And it is these things that the Disciples then preached in Judea, Samaria, and to the ends of the earth. Before the crucifixion Jesus said in Matthew 10:5-6 KJV
[5] “These twelve Jesus sent forth, and commanded them, saying, Go not into the way of the Gentiles, and into any city of the Samaritans enter ye not: [6] But go rather to the lost sheep of the house of Israel.”
After the resurrection He now sends them to Samaria and the whole world. Old covenant, law of Moses, Israel. New covenant, better promises, whole world.