The return of Elijah as a forerunner to the Messiah was commonly believed in Jesus' time. When Jesus asks his disciples, "Who do people say that I am?" all three Synoptic Gospels report that the disciples mention Elijah as one of the answers they have heard (Matthew 16:14; Mark 8:28; Luke 9:18-19).
In the Gospel of John, John the Baptist denies being Elijah (1:21), but in Matthew, after John the Baptist has been killed, Jesus clearly identifies Elijah with John (17:10-13; compare the parallel account, Mark 9:11-13).
The widely held speculation about Elijah's return is also reflected following the death of John the Baptist. When reports of Jesus' miraculous cures became known following John's death, some thought Jesus himself was John the Baptist or Elijah returning (Mark 6:14-16).
Malachi writes that when Elijah returns, "he will turn the hearts of parents to their children and the hearts of children to their parents" (Malachi 4:6). At the beginning of Luke's Gospel, the angel cites this verse to describe to Zechariah that his son John will fulfill Elijah's task: "With the spirit and power of Elijah he will go before him [the Lord], to turn the hearts of parents to their children, and the disobedient to the wisdom of the righteous, to make ready a people prepared for the Lord" (Luke 1:17).
With these verses about Elijah's return occurring both at the conclusion of the Old Testament and at the beginning of the Gospels, the figure of Elijah becomes a clear link between the Old and New Testaments.
5 Lo, I will send you the prophet Elijah before the great and terrible day of the Lord comes. 6He will turn the hearts of parents to their children and the hearts of children to their parents, so that I will not come and strike the land with a curse.*
New Revised Standard Version Bible: Anglicized Edition, copyright © 1989, 1995 National Council of the Churches of Christ in the United States of America. Used by permission. All rights reserved worldwide. http://nrsvbibles.org