What does Mark 9:9 mean?
Jesus almost always tells those He heals to keep their miracles to themselves (Mark 1:44; 5:43). He also keeps demons and the disciples from identifying His divine identity in public (Mark 1:25; 3:11–12; 8:29–30). Here, He insists Peter, James, and John hold back the description of His glory and God's words. The only significant information Jesus allows to share is that He will be killed and raised again (Mark 8:31).Part of the reason Jesus keeps the disciples from spreading the word that He is the Messiah is that they don't understand what the Messiah is. They know that the Messiah will rescue Israel. The desire for the Jews to be independent is so strong they try to force Him to be king (John 6:15) and will greet Him in Jerusalem as if He is already king (Mark 11:7–10).
Jesus affirms that this is His due when He refers to Himself as the "Son of Man." The title is from Daniel 7:13–14, a prophecy about "one like the son of man" who will be given dominion over the earth by the Ancient of Days. The disciples don't understand that this is not Jesus' only title.
God has just witnessed that Jesus is the Son of God (Mark 9:7). Jesus is that member of the Trinity who submits His will to God the Father, even as He deserves equal glory and honor (Philippians 2:6–8). But He is also the Suffering Servant of Isaiah 53. The Jews forfeited their independence when they rebelled against God (2 Kings 21:10–14). The disciples don't yet understand why their God-promised Savior would suffer not for their nation, but for their sins against God.