John 1:8

He was not the light; he came to testify to the light.

John 1:20

He frankly admitted, and did not try at all to deny it; yes, he frankly admitted, "I am not the Christ."

John 3:28

You can bear testimony to me yourselves that I said, 'I am not the Christ, but I have been sent as His announcer.'

Acts 19:4

Then Paul said, "John baptized with a baptism that was an expression of repentance, telling the people to believe in Him who was to come after him; that is, in 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
He frankly admitted, and did not try at all to deny it; yes, he frankly admitted, "I am not the Christ."
John 3:28
You can bear testimony to me yourselves that I said, 'I am not the Christ, but I have been sent as His announcer.'
Acts 19:4
Then Paul said, "John baptized with a baptism that was an expression of repentance, telling the people to believe in Him who was to come after him; that is, in Jesus."

General references

Mark 11:30
Was John's baptism from heaven or from men? Answer me."
Acts 13:24
as John, before His coming, had already preached baptism as an expression of repentance, for all the people of Israel.