Matthew 17:13
Then the disciples understood that he was speaking to them of John the Baptist. The disciples' understanding that Elijah = John the Baptist connects the transfiguration's Elijah-appearance and the scribal Elijah-must-come-first teaching. The understanding that the disciples reach in verse 13 is the same understanding that Matthew 11:14 offered: John is the Elijah who is to come, if you are willing to accept it.