Malachi 4:5-6

Behold, I will send you Elijah the prophet before the great and terrible day of the Lord comes. [Matt. 11:14; 17:10-13.] And he shall turn and reconcile the hearts of the [estranged] fathers to the [ungodly] children, and the hearts of the [rebellious] children to [the piety of] their fathers [a reconciliation produced by repentance of the ungodly], lest I come and smite the land with a curse and a ban of utter destruction. [Luke 1:17.]