Because Elijah did not die but was taken up, tradition looked for his return. The book of Malachi, closing the prophetic canon, promises that God will send Elijah before the great and terrible day of the Lord, to turn the hearts of parents and children to one another, making him the herald of the messianic age.
In Judaism this expectation runs deep in ritual and folklore. A cup of Elijah is poured at the Passover seder and the door opened for him; a chair for Elijah is set at every circumcision; and countless legends have him appear, unrecognized, to teach, rescue and test. He is the prophet of the world to come, whose coming will resolve disputed questions and announce redemption.
Christianity wove Elijah into its own story. He appears with Moses at the Transfiguration, conversing with Jesus, the prophets and the law bearing witness, and the Gospels present John the Baptist as the returning Elijah who prepares the messiah's way, a role John himself, in the Gospel of John, declines to claim in those literal terms.
Islam honours Ilyas among the prophets, upholding the worship of the one God against Baal. Across the traditions Elijah remains the zealous prophet and the awaited forerunner, poised between a first departure and a promised return.