Marcos 9:13

The disciples thought Elijah still had to come, but Jesus explained that he had come. His enemies had done to him what the Old Testament recorded. Jesus was speaking of John the Baptist (Matthew 17:13). The Old Testament passage to which Jesus referred was 1 Kings 19:1-3; 1 Kings 19:10. There Ahab, and especially Jezebel, swore to kill Elijah. They "wished" to execute him. This is exactly what "King" Herod Antipas, and especially Herodias, really did to John the Baptist. Now we see why Mark recorded the story of John’s death (Mark 6:17-29). It was to show that John the Baptist fulfilled the prophecies about Elijah coming.

"In this case Scripture had foretold the future not by prophecy but by a type. The fate intended for Elijah (I Kings xix. 2, 10) had overtaken John." [Note: Swete, p. 194.]

Evidently Mark did not mention John the Baptist as the fulfillment of this prophecy, as Matthew did, because his identity is obvious to the careful reader. The fulfillment was not complete, however, because someone will come in the spirit and power of Elijah to prepare the way before Messiah’s second coming (Malachi 4:5; cf. Revelation 11).

This discussion clarified for the disciples and for Mark’s readers how Jesus’ messiahship harmonized with Old Testament prophecy that seems to contradict it. Disciples of Jesus must have no doubts about His being the Son of Man, especially since they can anticipate testing through suffering for their faith. The importance of strong faith comes through in the next incident that Mark narrated.