For witness (ei marturian). Old word from marturew (from martu), both more common in John's writings than the rest of the N.T. This the purpose of the Baptist's ministry. That he might bear witness (ina marturhsh). Final clause with ina and aorist active subjunctive of marturew to make clearer ei marturian. Of the light (peri tou pwto). "Concerning the light." The light was shining and men with blinded eyes were not seeing the light ( John 1:26 ), blinded by the god of this world still ( 2 Corinthians 4:4 ). John had his own eyes opened so that he saw and told what he saw. That is the mission of every preacher of Christ. But he must first have his own eyes opened. That all might believe (ina pisteuswsin). Final clause with ina and first aorist active subjunctive of pisteuw, ingressive aorist "come to believe." This is one of John's great words (about 100 times), "with nine times the frequency with which it is used by the Synoptists" (Bernard). And yet pisti, so common in Paul, John uses only in 1 John 5:4 and four times in the Apocalypse where pisteuw does not occur at all. Here it is used absolutely as in John 1:50 , etc. Through him (di autou). As the intermediate agent in winning men to believe in Christ (the Logos) as the Light and the Life of men. This is likewise the purpose of the author of this book ( John 20:31 ). The preacher is merely the herald to point men to Christ.