Malachi 4:5-6
"Behold, I will send you Elijah the prophet before the coming of the great and dreadful day of the LORD: 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."

...............As Elijah was a voice that called Israel back to God in the days of the Old Testament, he and the other witness will call them again.

...............As Elijah called fire out of heaven, pronounced drought, punished the false prophets, and called for Israel to return to God, he will do it again.