“He was not that Light, but was sent to bear witness of that Light.”
King James Version (KJV)
1:6 There was a man - The evangelist now proceeds to him who testified of the light, which he had spoken of in the five preceding verses.
1:7 The same came for (that is, in order to give) a testimony - The evangelist, with the most strong and tender affection, interweaves his own testimony with that of John, by noble digressions, wherein he explains the office of the Baptist; partly premises and partly subjoins a farther explication to his short sentences. What St. Matthew, Mark, and Luke term the Gospel, in respect of the promise going before, St. John usually terms the testimony, intimating the certain knowledge of the relator; to testify of the light - Of Christ.
1:9 Who lighteth every man - By what is vulgarly termed natural conscience, pointing out at least the general lines of good and evil. And this light, if man did not hinder, would shine more and more to the perfect day.
1:10 He was in the world - Even from the creation.
Joh 1:8 He was not that Light, but [was sent] to bear testimony. An early heretical sect held that John the Baptist was the Messiah. The apostle is explicit, in order to correct this error.