He himself wasn’t the light, but his mission was to testify concerning the light.
He was not that Light, but was sent to bear witness of that Light.
He was not the Light himself, but came that he might bear witness regarding the Light.
He was not the light, but came that he might bear witness of the light.
He was not the Light, but he was to offer testimony about the Light.
He was not the light, but was to give testimony of the light.
