In the Old Testament, God promises to send a special messenger to announce the Messiah’s arrival (Isaiah 40:3-5; Malachi 3:1). That turns out to be John the Baptizer, the public “voice” for God.
And the child grew and became strong in spirit, and he was in the wilderness until the day of his public appearance to Israel…. As it is written in the book of the words of Isaiah the prophet, “The voice of one crying in the wilderness: ‘Prepare the way of the Lord, make His paths straight’” (Luke 1:80; 3:4).
John does not know ahead of time the identity of the Messiah. God gives John a sign: The One on whom the Spirit descends is He, the Son of God (John 1:29-34). Twice, God audibly confirms His choice.
The Holy Spirit descended on Him in bodily form, like a dove; and a voice came from heaven, “You are My beloved Son; with You I am well pleased” (Luke 3:22).
And a voice came out of the cloud, saying, “This is My Son, My Chosen One; listen to Him!” (Luke 9:35)