4 “Darkness was upon the face of the deep.” A new source for fables and most impious imaginations if one distorts the sense of these words at the will of one's fancies. By “darkness” these wicked men do not understand what is meant in reality— air not illumined, the shadow produced by the interposition of a body, or finally a place for some reason deprived of light. For them “darkness” is an evil power, or rather the personification of evil, having his origin in himself in opposition to, and in perpetual struggle with, the goodness of God. If God is light, they say, without any doubt the power which struggles against Him must be darkness, “Darkness” not owing its existence to a foreign origin, but an evil existing by itself. “Darkness” is the enemy of souls, the primary cause of death, the adversary of virtue. The words of the Prophet, they say in their error, show that it exists and that it does not proceed from God. From this what perverse and impious dogmas have been imagined! What grievous wolves, tearing the flock of the Lord, have sprung from these words to cast themselves upon souls! Is it not from hence that have come forth Marcions and Valentini, and the detestable heresy of the Manicheans, which you may without going far wrong call the putrid humour of the churches.
O man, why wander thus from the truth, and imagine for yourself that which will cause your perdition? The word is simple and within the comprehension of all. “The earth was invisible.” Why? Because the “deep” was spread over its surface. What is “the deep”? A mass of water of extreme depth. But we know that we can see many bodies through clear and transparent water. How then was it that no part of the earth appeared through the water? Because the air which surrounded it was still without light and in darkness. The rays of the sun, penetrating the water, often allow us to see the pebbles which form the bed of the river, but in a dark night it is impossible for our glance to penetrate under the water. Thus, these words “the earth was invisible” are explained by those that follow; “the deep” covered it and itself was in darkness. Thus, the deep is not a multitude of hostile powers, as has been imagined; nor “darkness” an evil sovereign force in enmity with good. In reality two rival principles of equal power, if engaged without ceasing in a war of mutual attacks, will end in self destruction. But if one should gain the mastery it would completely annihilate the conquered. Thus, to maintain the balance in the struggle between good and evil is to represent them as engaged in a war without end and in perpetual destruction, where the opponents are at the same time conquerors and conquered. If good is the stronger, what is there to prevent evil being completely annihilated? But if that be the case, the very utterance of which is impious, I ask myself how it is that they themselves are not filled with horror to think that they have imagined such abominable blasphemies.
It is equally impious to say that evil has its origin from God; because the contrary cannot proceed from its contrary. Life does not engender death; darkness is not the origin of light; sickness is not the maker of health. In the changes of conditions there are transitions from one condition to the contrary; but in genesis each being proceeds from its like, and not from its contrary. If then evil is neither uncreate nor created by God, from whence comes its nature? Certainly that evil exists, no one living in the world will deny. What shall we say then? Evil is not a living animated essence; it is the condition of the soul opposed to virtue, developed in the careless on account of their falling away from good.
Source: Nine Homilies of Hexaemeron (New Advent)