For this is he spoken of by Isaiah the prophet, saying: “The voice of one crying in the deserted place: Prepare the way of the Lord! Make His paths straight!” Isa. 40:3
Behold, I am sending My messenger, and He will clear the way before Me. And the Lord whom you are seeking shall suddenly come to His temple, even the Angel of the Covenant, in whom you delight. Behold, He comes, says Jehovah of Hosts.
And he will go ahead before Him in the spirit and power of Elijah “to turn the hearts of fathers to their children,” and disobedient ones to the wisdom of the just, to make ready a people having been prepared for the Lord. Mal. 4:5, 6