Thank you for asking a question on This is your Bible.
This was the question that the priests and Levites from Jerusalem asked John.
John 1:21 And they asked him, What then? Art thou Elias?
Which John answered in the negative.
And he saith, I am not.
John was to precede the messiah in the ‘spirit and power’ of Elijah.
Luke 1:17 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 then was not Elijah, but a type of Elijah who came before Christ at his first coming.
His mission was only partially successful in that although many of the Jews accepted Christ as their Messiah the majority would not.
Hence they were subjected to AD70 and 2000 years of dispersion and persecution.
Elijah himself will be sent to the Jews prior to Christ’s second coming.
Malachi 4:5 Behold, I will send you Elijah the prophet before the coming of the great and dreadful day of the LORD:
6 And he shall turn the heart of the fathers to the children, and the heart of the children to their fathers, lest I come and smite the earth with a curse.
The disciples asked Jesus a similar question because the Jews argued that Jesus was not the Messiah because Elijah had not come.
Matthew 17:10 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.
In saying ‘Elias truly shall first come’ Christ is confirming a future fulfilment of the words of Malachi.
When he says ‘Elias is come already’ we can reasonably understand this to mean that John came as a type of Elijah.
We know from Zechariah 12that when Christ comes again the Jews will recognise him as their Messiah.
Zechariah 12:10 And I will pour upon the house of David, and upon the inhabitants of Jerusalem, the spirit of grace and of supplications: and they shall look upon me whom they have pierced, and they shall mourn for him, as one mourneth for his only son, and shall be in bitterness for him, as one that is in bitterness for his firstborn.
We might conclude from this that Elijah will be successful, and God will bless rather than ‘smite the earth (Hebrew ‘eretz’ earth or land) with a curse’.
Isaiah 19:24 In that day shall Israel be the third with Egypt and with Assyria, even a blessing in the midst of the land (‘eretz’):
I hope this helps.