The entire gospel of John is a testimony to who Jesus is, and the first to testify is John the Baptist. He rejects any messianic designation for himself; rather his role is to prepare the way for another whom God would send.
That one has already come, but He is not recognized yet by anyone. He is initially not even recognized by John. It took a revelation from God to reveal the identity of Jesus to John. The true identity of Jesus must be revealed to us if we are to know Him – and revealing Jesus’ identity is the purpose of this gospel.
The importance of John the Baptist for us is that he reminds us that Jesus did not appear out of the blue, making incredible claims for Himself. God worked for centuries to prepare the world to receive His Son. He worked through the great events of the Old Testament and through the prophets to bring the Messiah and prepare the world for His coming. As the Messiah was near, God used John the Baptist to make the final arrangements and point out to us our Savior.
Once again, as the Church prepares to celebrate the coming of Christ at Christmas, the Church presents John the Baptist as His messenger to us. Then we can join Him once again and proclaim the message to others that Jesus Christ is the Son of God and Lord of All.