John 1:8

“He was not that light, etc.] He was a light; he was the forerunner of the sun of righteousness, the “phosphorus” of the Gospel day; he had great light in him; he knew that the Messiah was ready to come, and declared it; and upon his baptism he knew him personally, and signified him to others: he had great light into the person and work of Christ; and into the way of salvation by him, and remission of sins through him; into the doctrines of faith in Christ, and of evangelical repentance towards God; and into the abolition of the legal Mosaic and Jewish dispensation; and was an instrument of giving light to others; yea, he was a burning and shining light, in whose light the Jews rejoiced, at…”

“not that Light--(See on Joh 5:35). What a testimony to John to have to explain that "he was not that Light!" Yet was he but a foil to set it off, his night-taper dwindling before the Dayspring from on high (Joh 3:30).”

“For a witness - To give testimony. He came to prepare the minds of the people to receive him Matthew 3:0; Luke 3:0; to lead them by repentance to God; and to point out the Messiah to Israel when he came, John 1:31. Of the Light - That is, of the Messiah. Compare Isaiah 60:1. That all men ... - It was the object of John’s testimony that all people might believe. He designed to prepare them for it; to announce that the Messiah was about to come, to direct the minds of men to him, and thus to prepare them to believe on him when he came. Thus, he baptized them, saying “That they should believe on him who should come after him” Acts 19:4, and thus he produced a very general expectation that the…”

“1:8 Some Jews speculated that John the Baptist was the Messiah; some of his followers were even reluctant to follow Jesus (3:22-30). However, John the Baptist was not the light; his role was to announce Jesus (1:19-34).”

“that light: Joh 1:20, Joh 3:28; Act 19:4 John 1:9”