Matthew 17: 10-13: "And his disciples asked him, saying, Why then say the scribes that Elias must first come? 11. And Jesus answered and said unto them, Elias truly shall first come, and restore all things. 12. But I say unto you, That Elias is come already, and they knew him not, but have done unto him whatsoever they listed. Likewise shall also the Son of man suffer of them. 13. Then the disciples understood that he spake unto them of John the Baptist"
Matthew 17: 10-13 shows us the big difference between the physical literalism of the Scribes and Pharisees and the spiritual interpretation of Jesus Christ. Christ did not expect a literal appearing of Elijah. John the Baptist came in the spirit and power of Elijah.
Luke 1: 17 tells us about the mission of John the Baptist. "And he shall go before him in the spirit and power of Elias, to turn the hearts of the fathers to the children, and the disobedient to the wisdom of the just; to make ready a people prepared for the Lord."
John the Baptist came in the spirit and power of Elijah, to turn the hearts of the disobedient to the wisdom of the just and to prepare the people for the coming of the Lord.
"And this is the record of John, when the Jews sent priests and Levites from Jerusalem to ask him, Who art thou? 20. And he confessed, and denied not; but confessed, I am not the Christ.
21. And they asked him, What then? Art thou Elias? And he saith, I am not. Art thou that prophet? And he answered, No. 22. Then said they unto him, Who art thou? that we may give an answer to them that sent us. What sayest thou of thyself? 23. He said, I am the voice of one crying in the wilderness, Make straight the way of the Lord, as said the prophet Esaias." John 1: 19-23
The Pharisees were stuck in the physical and literal and did not understand that which is spiritual, that John the Baptist came in the spirit of Elijah.
"The voice of him that crieth in the wilderness, Prepare ye the way of the LORD, make straight in the desert a highway for our God." Isaiah 40: 3
In the spirit of the prophet Elijah, John the Baptist called the people to repent from their sins, sought to prepare them to believe in Christ, become born again in him and to believe and follow his doctrines. John the Baptist was also calling them out of the religion of the Pharisees.
"But when he saw many of the Pharisees and Sadducees come to his baptism, he said unto them, O generation of vipers, who hath warned you to flee from the wrath to come? 8. Bring forth therefore fruits meet for repentance: 9. And think not to say within yourselves, We have Abraham to our father: for I say unto you, that God is able of these stones to raise up children unto Abraham. 10. And now also the axe is laid unto the root of the trees: therefore every tree which bringeth not forth good fruit is hewn down, and cast into the fire." Matthew 3: 7-10
John the Baptist called the Pharisees vipers, told them to repent and not to claim that they were of the physical bloodline from Abraham, and uses the metaphor of an ax laid to the trees, saying that the religious teachings of the Pharisees were to be done away with.
The appearing of John the Baptist in the spirit and power of Elijah to prepare people for the first coming of the Lord does not necessarily exhaust totally the prophecy of Malachi 4: 5-6, "Behold,I will send you Elijah the prophet before the coming of the great and dreadful day of the Lord."
The spirit and power of Elijah will appear in the remnant - seen in Revelation 7 and Revelation 14 and in Revelation 12: 15-17 - in the end time before Christ himself appears.
Again, the spirit and power of Elijah will appear to prepare the people of God for the coming of the Lord. "And the dragon was wroth with the woman, and went to make war with the remnant of her seed, which keep the commandments of God, and have the testimony of Jesus Christ." Revelation 12: 17
"These are they which were not defiled with women; for they are virgins. These are they which follow the Lamb whithersoever he goeth. These were redeemed from among men, being the firstfruits unto God and to the Lamb. 5. And in their mouth was found no guile: for they are without fault before the throne of God." Revelation 14: 4-5