Yet every just man, every holy man in the Church, for all that he is glad to be enlightened, sees that to a great extent he is still in darkness, and he is saddened by this. Of necessity therefore, although he is enlightened, he asks to be enlightened still more. For the more his lamp is enlightened, the more truly is his darkness revealed to him by the lamp itself. Do not immediately consider as opposed to this the words of incarnate Truth in the gospel: “The lamp of your body is your eye. If your eye is clear your whole body will be lit up.” For it does not follow that because the whole of our activity is lit up by the eye of a pure intention all the darkness of our mistaken opinions and ignorant views is immediately enlightened. The measure of our enlightenment is still this, that the man who is able to know his own inadequacy and recognize what it lacking to him is to be judged as having made great progress towards the light of truth. Hence it is that among the wise men of this world whose disquisitions on the subject of knowledge are the most marked by sobriety the first degree of knowledge is reckoned as knowing one’s own ignorance.
Guerric of Igny, Liturgical Sermons I, Sermon 13: The Third Sermon for the Epiphany