So, once upon a time, there was a guy named Jesus who walked around and taught people about God. One day, he took his good friends Peter, James, and John to a mountain to pray. While they were praying, something really amazing happened. Jesus started to glow and his clothes became super bright like the sun.
Then, two other people named Moses and Elijah appeared and talked with Jesus. They were very important people from the past who had died but were now in heaven. The friends were really scared, but Jesus told them not to be afraid.
They all saw this amazing thing happening and heard God's voice saying, "This is my Son, whom I love; with him, I am well pleased. Listen to him!" Then Jesus went back to his normal self, and they all came down the mountain.
So, the transfiguration of Jesus is when he showed his friends that he was not just a regular person, but the Son of God. He became very bright and talked with two great people from the past, and God himself spoke from heaven. The friends saw something amazing and learned that Jesus was really special.