John the Baptist's metaphorical statement about himself in the Gospel of John has a corresponding detail in the circumstances of his birth, and a corresponding "sign" (miracle).
The voice of him that crieth in the wilderness, Prepare ye the way of the LORD, make straight in the desert a highway for our God.
Isaiah 40:3
John's statement in the Gospel of John:
"I am the voice of one crying in the wilderness, Make straight the way of the Lord, as said the prophet Esaias." Isaiah 40:3, John 1:23
Corresponding detail in the circumstances of John's birth:
John's father, Zacharias, lost his voice when the angel Gabriel appeared to him and announced to him that his wife would bear a son, and that his name would be John. He recovered his voice after John was born, when he wrote on a tablet, "His name is John." Luke 1:5-25, 57-64
John the Baptist was a "voice" because he identified Jesus as the Messiah, and publicly proclaimed him to be the Messiah. One of John's disciples was Andrew, Simon Peter's brother, who told him that the Messiah had been found, and brought him to Jesus. John 1:40-42
"I am the voice of one crying in the wilderness, Make straight the way of the Lord, as said the prophet Esaias." Isaiah 40:3, John 1:23
