Every just man, every holy man in the Church, for all that he is glad to be enlightened, sees that he is in darkness to a great extent and is saddened by this. Although he is enlightened, he necessarily asks to be still more enlightened; for the more his lamp is filled with light the more his darkness is truly revealed to him by that very lamp. Do not immediately consider the words of the incarnate Truth opposed to this when the Gospel says, The lamp of your body is your eye; if your eye is clear your whole body will be light. For it does not follow that because the whole of our activity is illumined by the eye of 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 capable of knowing his own inadequacy and recognize what is lacking in him, is to be judged as having made great progress towards the light of truth. So it is that among the wise of this world, whose disquisitions on the subject of knowledge are marked by sobriety, the first degree of knowledge is reckoned as knowing one’s own ignorance.
From Guerric of Igny’s Third Sermon for the Epiphany (Liturgical Sermons 1, CF 8, Sermon 13, p. 84)