Testifying About the Light

“There was a man sent from God, whose name was John.
The same came for a witness, to bear witness of the Light,
that all men through him might believe.
He was not that Light, but was sent to bear witness of that Light.”
John 1:6–8

John is showing that Jesus of Nazareth is the Messiah, God’s Son, and we must believe on Him (John 20:31). Jesus is God, has always existed, and has created the universe. God the Father sent Him to earth as the true Light of Life, but no one even noticed.
God also sent another man, John, ahead of Jesus to testify about the coming of God’s Light. We usually call this man “John the Baptist,” or better, “John the Baptizer.” He was distinguished from many others with the same name because his ministry was one of baptizing people as a sign of repentance (Mark 1:4).
Our verses say that John was not the Messiah, although he was asked about this several times (John 1:19–25). Rather, he was a forerunner, in the words Mark uses from Malachi, “Behold, I send my messenger before thy face, which shall prepare thy way before thee” (Mark 1:2). He came to testify about the Light of the World. He came proclaiming that Someone greater was coming (1:26–27). He called on those who heard him to believe on Jesus (John 1:29). He sent his disciples to Jesus (Luke 7:19–23). God sent John the Baptist to testify about the Light of Life, Jesus of Nazareth. John’s mission was to prepare the way for Jesus, and to show that He was the Messiah.
This is the gospel writer’s goal, too: to prove that Jesus of Nazareth is the Messiah, so that his readers will believe in Him. God sent His Son into the world to give life, and we must believe in Him.