What does Mark 9:8 mean?

Jesus takes Peter, James, and John to a high mountain to witness His transfiguration. Jesus' clothes become brilliantly white while He speaks with Moses and Elijah. The shekinah glory of God surrounds them, and God affirms Jesus' identity as His Son. Now, the three disciples are again alone with their rabbi.

Peter has acknowledged that Jesus is the promised Messiah, but the disciples aren't afraid of Him. They're afraid of Moses, Elijah, and the glory that surrounds Jesus. They're afraid when God speaks. When it's just Jesus, they're afraid of irritating Him (Mark 8:16), but they still don't understand that He is God with all the power and authority of the Jewish YWHW. It won't be until after the resurrection, when Jesus appears alive and whole and walking through walls that they will begin to understand that they are not to fear men like Moses and Elijah, but the Lord their God (Luke 24:25–27).

People today tend to act similarly. Jesus teaches that we should love our neighbor (Mark 12:31), serve those who can do nothing for us (Luke 14:12–14), and honor pure hearts over deep wallets (Mark 12:41–44). He suffered and died for our sins. Many people see Jesus as a gentle and loving teacher—which He is—but they stop there. They don't understand that the sinlessness of Jesus doesn't just mean He's kind, it means He's the all-holy God. Much of Jesus' ministry is to explain to His disciples who He is.