John 1:8

that one was not the Light, but -- that he might testify about the Light.

John 1:20

and he confessed and did not deny, and confessed -- 'I am not the Christ.'

John 3:28

ye yourselves do testify to me that I said, I am not the Christ, but, that I am having been sent before him;

Acts 19:4

And Paul said, 'John, indeed, did baptize with a baptism of reformation, saying to the people that in him who is coming after him they should believe -- that is, in the Christ -- Jesus;'

Treasury of Scripture Knowledge

Summary

He was not that Light, but was sent to bear witness of that Light.

General references

Bible References

That light

John 1:20
and he confessed and did not deny, and confessed -- 'I am not the Christ.'
John 3:28
ye yourselves do testify to me that I said, I am not the Christ, but, that I am having been sent before him;
Acts 19:4
And Paul said, 'John, indeed, did baptize with a baptism of reformation, saying to the people that in him who is coming after him they should believe -- that is, in the Christ -- Jesus;'

General references

Mark 11:30
the baptism of John -- from heaven was it? or from men? answer me.'
Acts 13:24
John having first preached, before his coming, a baptism of reformation to all the people of Israel;