Genesis 1:6

6Let there be a firmament (58) The work of the second day is to provide an empty space around the circumference of the earth, that heaven and earth may not be mixed together. For since the proverb, ‘to mingle heaven and earth,’ denotes the extreme of disorder, this distinction ought to be regarded as of great importance. Moreover, the word רקיע (rakia) comprehends not only the whole region of the air, but whatever is open above us: as the word heaven is sometimes understood by the Latins. Thus the arrangement, as well of the heavens as of the lower atmosphere, is called רקיע (rakia) without discrimination between them, but sometimes the word signifies both together sometimes one part only, as will appear more plainly in our progress. I know not why the Greeks have chosen to render the word ςτερέωμα, which the Latins have imitated in the term, firmamentum ; (59) for literally it means expanse. And to this David alludes when he says that ‘the heavens are stretched out by God like a curtain,’ (Psalms 104:2.) If any one should inquire whether this vacuity did not previously exist, I answer, however true it may be that all parts of the earth were not overflowed by the waters; yet now, for the first time, a separation was ordained, whereas a confused admixture had previously existed. Moses describes the special use of this expanse, to divide the waters from the waters from which word arises a great difficulty. For it appears opposed to common sense, and quite incredible, that there should be waters above the heaven. Hence some resort to allegory, and philosophize concerning angels; but quite beside the purpose. For, to my mind, this is a certain principle, that nothing is here treated of but the visible form of the world. He who would learn astronomy, (60) and other recondite arts, let him go elsewhere. Here the Spirit of God would teach all men without exception; and therefore what Gregory declares falsely and in vain respecting statues and pictures is truly applicable to the history of the creation, namely, that it is the book of the unlearned. (61) The things, therefore, which he relates, serve as the garniture of that theater which he places before our eyes. Whence I conclude, that the waters here meant are such as the rude and unlearned may perceive. The assertion of some, that they embrace by faith what they have read concerning the waters above the heavens, notwithstanding their ignorance respecting them, is not in accordance with the design of Moses. And truly a longer inquiry into a matter open and manifest is superfluous. We see that the clouds suspended in the air, which threaten to fall upon our heads, yet leave us space to breathe. (62) They who deny that this is effected by the wonderful providence of God, are vainly inflated with the folly of their own minds. We know, indeed that the rain is naturally produced; but the deluge sufficiently shows how speedily we might be overwhelmed by the bursting of the clouds, unless the cataracts of heaven were closed by the hand of God. Nor does David rashly recount this among His miracles, that God layeth the beams of his chambers in the waters, (Psalms 104:31;) and he elsewhere calls upon the celestial waters to praise God, (Psalms 148:4.) Since, therefore, God has created the clouds, and assigned them a region above us, it ought not to be forgotten that they are restrained by the power of God, lest, gushing forth with sudden violence, they should swallow us up: and especially since no other barrier is opposed to them than the liquid and yielding, air, which would easily give way unless this word prevailed, ‘Let there be an expanse between the waters.’ Yet Moses has not affixed to the work of this day the note that God saw that it was good: perhaps because there was no advantage from it till the terrestrial waters were gathered into their proper place, which was done on the next day, and therefore it is there twice repeated. (63)