John 1:8

he was not that Light, but was sent to testify of that light.

John 1:20

he own'd it, and did not deny it; but made this protestation, I am not the Christ.

John 3:28

you yourselves can bear me witness, that I said, I am not the Christ, but was only sent before him:

Acts 19:4

upon which Paul said, John indeed administer'd the baptism of repentance, but with this admonition, that they should believe in him, who was to come after, that is, in Jesus the Messias.

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 own'd it, and did not deny it; but made this protestation, I am not the Christ.
John 3:28
you yourselves can bear me witness, that I said, I am not the Christ, but was only sent before him:
Acts 19:4
upon which Paul said, John indeed administer'd the baptism of repentance, but with this admonition, that they should believe in him, who was to come after, that is, in Jesus the Messias.

General references

Mark 11:30
the baptism of John, was it of divine, or of human institution?
Acts 13:24
before his appearance, John had preach'd the baptism of repentance to all the people of Israel.