Mt 17:9a, 10-13
9As they were coming down from the mountain, 10the disciples asked [Jesus], “Why do the scribes say that Elijah must come first?” 11He said in reply, “Elijah will indeed come and restore all things; 12but I tell you that Elijah has already come, and they did not recognize him but did to him whatever they pleased. So also will the Son of Man suffer at their hands.” 13Then the disciples understood that he was speaking to them of John the Baptist.
ELIJAH HAS ALREADY COME: The prophet Elijah was taken into heaven in a fiery whirlwind ride—“flaming chariot” driven by “flaming horses” (2 Kgs 2:11). He is expected to return to earth to prepare for the coming of the Lord (Mal 3:1, 23). Jewish tradition takes the prophecy literally: the prophet Elijah will return in the same spectacular manner that he left. This is one of the reasons the religious authorities of Israel do not recognize John the Baptist as fulfilling the role of the precursor of the Messiah. He is only an ordinary desert ascetic; there are no spectacular miracles in his life and he cannot offer any. All that he can show is a fiery preaching on the necessity of repentance and conversion.
Jesus denounces the religious authorities for their negative attitude toward John. In truth, John fulfills the role of the prophet Elijah according to divine terms. They reject him because they are uncomfortable with his message. They refuse to repent and be converted. So John the oppositor and “disturber” of the comfortable was eliminated. Herod Antipas had him imprisoned and beheaded. Jesus sees the persecution of John the Baptist and Elijah (persecuted by Jezebel and Ahab) as mark of their being genuine prophets. He has premonitions that he will suffer in the same way.