8 Behold, even lamps bear witness to the day, because of our weakness, for we cannot bear and look at the brightness of the day. In comparison, indeed, with unbelievers, we Christians are even now light; as the apostle says, “For you were once darkness, but now light in the Lord: walk as children of light:” and he says elsewhere, “The night is far spent, the day is at hand: let us therefore cast away the works of darkness, and put on us the armor of light; let us walk honestly as in the day.” Yet that even the day in which we now are is still night, in comparison with the light of that to which we are to come, listen to the Apostle Peter: he says that a voice came to the Lord Christ from the excellent glory, “You are my beloved Son, in whom I am well pleased.
This voice,” said he, “which came from heaven, we heard, when we were with Him in the holy mount.” But because we were not there, and have not then heard this voice from heaven, the same Peter says to us, “And we have a more sure word of prophecy.” You have not heard the voice come from heaven, but you have a more sure word of prophecy. For the Lord Jesus Christ, foreseeing that there would be certain wicked men who would calumniate His miracles, by attributing them to magical arts, sent prophets before Him.
For, supposing He was a magician, and by magical arts caused that He should be worshipped after His death, was He then a magician before He was born? Hear the prophets, O man dead, and breeding the worms of calumny, hear the prophets: I read, hear them who came before the Lord. “We have,” says the Apostle Peter, “a more sure word of prophecy, to which you do well to give heed, as to a lamp in a dark place, until the day dawn, and the day-star arise in your hearts.”
Source: Tractates on the Gospel of John (New Advent)