God said "Let there be light."

And God said, Let there be light: The first word of God created the nature of light; it made darkness vanish, dispelled gloom, illuminated the world, and gave to all beings at the same time a sweet and gracious aspect. The heavens, until then enveloped in darkness, appeared with that beauty which they still present to our eyes. The air was lighted up, or rather made the light circulate mixed with its substance, and, distributing its splendour rapidly in every direction, so dispersed itself to its extreme limits. Up it sprang to the very aether and heaven. In an instant it lighted up the whole extent of the world, the North and the South, the East and the West. For the aether also is such a subtle substance and so transparent that it needs not the space of a moment for light to pass through it. Just as it carries our sight instantaneously to the object of vision, so without the least interval, with a rapidity I that thought cannot conceive, it receives these rays of light in its uttermost limits. With light the aether becomes more pleasing and the waters more limpid. These last, not content with receiving its splendour, return it by the reflection of light and in all directions send forth quivering flashes. The divine word gives every object a more cheerful and a more attractive appearance, just as when men in deep sea pour in oil they make the place about them clear. So, with a single word and in one instant, the Creator of all things gave the boon of light to the world.


Let there be light. The order was itself an operation, and a state of things was brought into being, than which man's mind cannot even imagine a pleasanter one for our enjoyment. It must be well understood that when we speak of the voice, of the word, of the command of God, this divine language does not mean to us a sound which escapes from the organs of speech, a collision of air struck by the tongue; it is a simple sign of the will of God, and, if we give it the form of an order, it is only the better to impress the souls whom we instruct.


Excerpt from The Hexaemeron, Homily II of St. Basil the Great