What does Matthew 17:9 mean?
Jesus had taken Peter, James, and John up the mountain with Him. He meant for them to see Him in His glory, radiating light from His face and His clothes. He meant for them to see Him talking to Moses and Elijah. Their participation in this moment was intentional. It was intended to convince them and those they would tell that Jesus was truly the Son of God from heaven (Matthew 17:1–8). Now, though, as the four of them walk down the mountain together, Jesus commands them not to tell anyone for the moment. They must wait until He, the Son of Man, is raised from the dead.This is the final time Jesus will instruct His disciples not to reveal the deepest truths about His identity. Taken together, Jesus seems to want to avoid having the people of Israel revolt against Rome, attempting to make Him king by force. That is not the purpose of His mission (John 6:15). In addition, He means for His resurrection from the dead to be the central evidence to the people that He is the Son of God. This is the sign of Jonah that He has promised to the Jewish religious leaders (Matthew 12:39; 16:4). Perhaps He does not want the report of His glorious appearance on the mountain to overshadow that event.
Matthew doesn't mention it, but Mark's account of this moment reveals that Peter, James, and John were confused by Jesus' mention of His rising from the dead. They wondered what it meant (Mark 9:10). Though Jesus had told them repeatedly what He must soon do, they still did not understand it.