The Old Testament prophet Malachi lived many years before Jesus was born. Malachi had said that before the Messiah came a prophet named Elijah would return. Jesus explained that Malachi had been talking about John the Baptist. Jesus said this because John the Baptist had done what Malachi had said that Elijah would do. (See: [[rc://en/tw/dict/bible/kt/prophet]] and [[rc://en/tw/dict/bible/kt/christ]])
Scripture often speaks of God's glory as a great, brilliant light. When people see this light, they are afraid. Matthew says in this chapter that Jesus's body shone with this glorious light so that his followers could see that Jesus truly was God's Son. At the same time, God told them that Jesus was his Son. (See: [[rc://en/tw/dict/bible/kt/glory]] and [[rc://en/tw/dict/bible/kt/fear]])