Tractates on the Gospel of John

⁶ Wherefore then did he come? “But that he might bear witness concerning the light.” Why so? “That all might believe through him.” And concerning what light was he to bear witness? “That was the true light.” Wherefore is it added true? Because an enlightened man is also called a light; but the true light is that which enlightens. For even our eyes are called lights; and nevertheless, unless either during the night a lamp is lighted, or during the day the sun goes forth, these lights are open in vain.

Thus, therefore, John was a light, but not the true light; because, if not enlightened, he would have been darkness; but, by enlightenment, he became a light. For unless he had been enlightened he would have been darkness, as all those once impious men, to whom, as believers, the apostle said, “You were sometimes darkness.” But now, because they had believed, what?— “but now are you light,” he says, “in the Lord.” Unless he had added “in the Lord,” we should not have understood. “Light,” he says, “in the Lord:” darkness you were not in the Lord. “For you were sometimes darkness,” where he did not add in the Lord. Therefore, darkness in you, light in the Lord. And thus “he was not that light, but was sent to bear witness of the light.”