John the Baptist came preaching the coming of Jesus Christ (Matthew 3 and Mark 1).
John the Baptist was the Elias to come but the people did not understand this at the time.
Matthew 17:10-13: “And his disciples asked him, saying, Why then say the scribes that Elias must first come? And Jesus answered and said unto them, Elias truly shall first come, and restore all things. 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. Then the disciples understood that he spake unto them of John the Baptist.”
The Elijah to come in Malachi 4:5 will be the leader of the two witnesses in Revelation 11. This Elijah, along with the other witness, will prophesy of Jesus’ coming. Jesus will return shortly thereafter.
Malachi 4:5, “Behold, I will send you Elijah the prophet before the coming of the great and dreadful day of the Lord:”
Revelation 11:3: “And I will give power unto my two witnesses, and they shall prophesy a thousand, two hundred and threescore days, clothed in sackcloth.”
John the Baptist prepared the way for Jesus the first time prophesying of His coming. Likewise, the Elijah to come along with the other witness will prepare the way for the return of Jesus Christ.