By St. Gregory the Theologian
There is one Light, God: inaccessible, knowing no succession or beginning, never ceasing, never measured, always shining – triply shining! – yet few, I think or less than few, are capable of reflecting on how great it is. And there are secondary lights, shining forth from that first Light: the powers that surround it, the spirits that serve it. But this light around us not only began recently, but is interrupted by night, and itself interrupts night in equal measure; it is entrusted to our sight, it is poured out in the air, it takes the very thing it gives – for it provides sight for the power of seeing, and is the first thing that our eyes see; by bathing visible objects, it gives us access to them.
For since God has willed this universe, composed of both visible and invisible beings, be put together as the great and marvelous herald of his greatness, he himself is the light for eternal creatures, and there is no other (for why would those who possessed the greatest of lights need a second one?); but for lower creatures – those all around us – he caused the power of this light to shine forth, first of all.
For it was fitting that the Great Light begin the work of creation with light, by which he destroyed the darkness, along with the disorder and confusion that had prevailed until then.
He did not display this light in the beginning, in my opinion, through some instrument like the sun. It was disembodied, unconnected with a sun; only later was the sun given the work of shedding light on the whole world. For while, in the case of other creatures, he brought matter into being first and created form later, limiting each thing by order and shape and size, in this case – to work a still greater wonder – he caused the form to exist without the matter (for light is the form of the sun), and after this added the matter, creating the sun as the shining eye of day.
So one thing is numbered first in the list of days, another second and third and so on, until we reach the seventh day, which brings work to an end. The events of creation are divided up by these days, ordered in accord with God’s ineffable reasons, and not attributed all at once to the omnipotent Word, to whom merely thinking or speaking is a work completed.