The voice.

Isaiah 40:3-5
A voice of one calling: "Prepare the way for the LORD in the wilderness; make a straight highway for our God in the desert. . . .

Matthew 3:3
This is he who was spoken of through the prophet Isaiah: "A voice of one calling in the wilderness, 'Prepare the way for the Lord, make straight paths for Him.'"

Mark 1:3
"A voice of one calling in the wilderness, 'Prepare the way for the Lord, make straight paths for Him.'"

John 1:23
John replied in the words of Isaiah the prophet: "I am the voice of one calling in the wilderness, 'Make straight the way for the Lord.'"

Prepare.

Luke 1:16, 17, 76-79
Many of the sons of Israel he will turn back to the Lord their God. . . .

Isaiah 57:14
And it will be said, "Build it up, build it up, prepare the way, take every obstacle out of the way of My people."

Isaiah 62:10
Go out, go out through the gates; prepare the way for the people! Build it up, build up the highway; clear away the stones! Raise a banner for the nations to see.

Malachi 4:6
And he will turn the hearts of the fathers to their children, and the hearts of the children to their fathers. Otherwise, I will come and strike the land with a curse."

John 1:7, 26-36
He came as a witness to testify about the Light, so that through him everyone might believe. . . .

John 3:28-36
You yourselves can testify that I said, 'I am not the Christ, but am sent ahead of Him.' . . .