John 1:6-8

There was a man sent from God whose name was John. He came as a witness to testify concerning that light, so that through him all might believe. He himself was not the light; he came only as a witness to the light. 

There was a man sent from God whose name was John 
Matthew 3:1-3  In those days John the Baptist came, preaching in the wilderness of Judea and saying, "Repent, for the kingdom of heaven has come near." This is he who was spoken of through the prophet Isaiah: "A voice of one calling in the wilderness, 'Prepare the way for the Lord, make straight paths for him.' " [Isaiah 40:3]

He came as a witness to testify concerning that light 
John 1:15  (John testified concerning him. He cried out, saying, "This is the one I spoke about when I said, 'He who comes after me has surpassed me because he was before me.' ")
John 1:19-20  Now this was John's testimony when the Jewish leaders in Jerusalem sent priests and Levites to ask him who he was. He did not fail to confess, but confessed freely, "I am not the Messiah."
John 1:32  Then John gave this testimony: "I saw the Spirit come down from heaven as a dove and remain on him."
John 3:26  They [John's disciples] came to John and said to him, "Rabbi, that man who was with you on the other side of the Jordan--the one you testified about--look, he is baptizing, and everyone is going to him."
John 5:33  "You have sent to John and he has testified to the truth."

so that through him all might believe 
John 1:12  Yet to all who did receive him [the light], to those who believed in his name, he gave the right to become children of God--...
John 3:16  For God so loved the world that he gave his one and only Son, that whoever believes in him shall not perish but have eternal life.

He himself was not the light; he came only as a witness to the light 
John 1:23  John replied in the words of Isaiah the prophet, "I am the voice of one calling in the wilderness, 'Make straight the way for the Lord,' " [Isaiah 40:3]

[brackets are mine]

Scriptures taken from the Holy Bible, New International Version® NIV®, 
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