A voice cries:
“In the wilderness prepare the way of the LORD;
make straight in the desert a highway for our God.
Every valley shall be lifted up,
and every mountain and hill be made low;
the uneven ground shall become level,
and the rough places a plain.” Isaiah 40:3-4
Behold, I send my messenger, and he will prepare the way before me. And the Lord whom you seek will suddenly come to his temple; and the messenger of the covenant in whom you delight, behold, he is coming, says the LORD of hosts. Malachi 3:1
Behold, I will send you Elijah the prophet before the great and awesome day of the LORD comes. Malachi 4:5
As it is written in Isaiah the prophet,
“Behold, I send my messenger before your face,
who will prepare your way
the voice of one crying in the wilderness:
‘Prepare the way of the Lord,
make his paths straight,’” John appeared, baptizing in the wilderness and proclaiming a baptism of repentance for the forgiveness of sins. And all the country of Judea and all Jerusalem were going out to him and were being baptized by him in the river Jordan, confessing their sins. Now John was clothed with camel’s hair and wore a leather belt around his waist and ate locusts and wild honey. And he preached, saying, “After me comes he who is mightier than I, the strap of whose sandals I am not worthy to stoop down and untie. I have baptized you with water, but he will baptize you with the Holy Spirit.” Mark 1:2-8
This is he of whom it is written,
“‘Behold, I send my messenger before your face,
who will prepare your way before you.’ Truly, I say to you, among those born of women there has arisen no one greater than John the Baptist. Yet the one who is least in the kingdom of heaven is greater than he. From the days of John the Baptist until now the kingdom of heaven has suffered violence, and the violent take it by force. For all the Prophets and the Law prophesied until John and if you are willing to accept it, he is Elijah who is to come. Matthew 11:10-14
See also:
In those days John the Baptist came preaching in the wilderness of Judea “Repent, for the kingdom of heaven is at hand.”
For this is he who was spoken of by the prophet Isaiah when he said,
“The voice of one crying in the wilderness:
‘Prepare the way of the Lord;
make his paths straight.’” Matthew 3:1-3
And this is the testimony of John, when the Jews sent priests and Levites from Jerusalem to ask him, “Who are you?” (..) He said, “I am the voice of one crying out in the wilderness, ‘Make straight the way of the Lord,’ as the prophet Isaiah said.” John 1:19-23