Then the disciples understood that he was speaking to them about John the Baptist.
After Jesus’ explanation, the disciples finally understand that the prophecy about Elijah’s coming had been fulfilled not in a literal way, but in a spiritual sense, in the person of John the Baptist. They understand that John the Baptist was the sent prophet who had come to prepare the Lord’s way. Yet their understanding comes gradually, as a result of Christ’s guiding explanation, which shows that even the closest disciples at first struggled to distinguish between the figurative and the actual ways a prophecy is fulfilled.