5 Where was it? Was it here? Was it with the Father, and was it not here? Or, what is more true, was it both with the Father and here also? If then it was here, wherefore was it not seen? Because “the light shines in darkness, and the darkness comprehended it not.” Oh men, be not darkness, be not unbelieving, unjust, unrighteous, rapacious, avaricious lovers of this world: for these are the darkness. The light is not absent, but you are absent from the light. A blind man in the sunshine has the sun present to him, but is himself absent from the sun.
Be not then darkness. For this is perhaps the grace regarding which we are about to speak, that now we be no more darkness, and that the apostle may say to us, “We were sometime darkness, but now light in the Lord.” Because then the light of men was not seen, that is, the light of minds, there was a necessity that a man should give testimony regarding the light, who was not in darkness, but who was already enlightened; and nevertheless, because enlightened, not the light itself, “but that He might bear witness of the light.”
For “he was not that light.” And what was the light? “That was the true light which enlightened every man that comes into the world.” And where was that light? “In this world it was.” And how was it “in this world?” As the light of the sun, of the moon, and of lamps, was that light thus in the world? No. Because “the world was made by Him, and the world knew Him not;” that is to say, “the light shines in darkness, and the darkness comprehended it not.” For the world is darkness; because the lovers of the world are the world.
For did not the creature acknowledge its Creator? The heavens gave testimony by a star; the sea gave testimony, and bore its Lord when He walked upon it; the winds gave testimony, and were quiet at His bidding; the earth gave testimony, and trembled when He was crucified. If all these gave testimony, in what sense did the world not know Him, unless that the world signifies the lovers of the world, those who with their hearts dwell in the world? And the world is evil, because the inhabitants of the world are evil; just as a house is evil, not because of its walls, but because of its inhabitants.
Source: Tractates on the Gospel of John (New Advent)