Studies in Genesis 1
And God said, “Let there be an expanse in the midst of the waters, and let it separate the waters from the waters.” And God made the expanse and separated the waters that were under the expanse from the waters that were above the expanse. And it was so. And God called the expanse Heaven. And there was evening and there was morning, the second day. (Genesis 1:6-8 ESV)
From the beginning of creation through its end God established a principle of separation.
God separated that which is below from that which is above. He made a “firmament” which may better be translated “expanse” but which means much more than expanse. It can mean a solid surface, a flat base or support, or the space above a solid, firm surface. On the earth it is the solid surface which supports the waters, the oceans, lakes and rivers.
God calls the expanse above the earth “Heaven” which could be simply the atmosphere which surrounds the earth and holds the gaseous waters for rain. Beyond the atmosphere the Sun, Moon and stars are placed. So, the firmament is the expanse above the earth which includes the atmosphere and everything else surrounding the earth in the universe.
God uses the word “water” five times in these two verses. “Water” does not mean the chemical compound H2O as we know water. Here, water means a liquid “juice” such as urine. It is a waste, a dangerous mixture some have called a “primordial soup.” God separated that which is good, wholesome and healthy, that which is needed to sustain life, from that which is dangerous and adverse to any and all life. Without knowing exactly how He does this it would seem He begins to strain the hazardous liquid through the atmosphere to separate that which is good for life from that which is deleterious to life.
God separates out the earth, a place which He will fill with life, from the rest of the universe. He names the atmosphere and everything beyond it just as He named the period of time of light and darkness. God separates out the chemicals needed to sustain life from those which are adverse and kill life. God separates the solid earth, a small speck of dust in a beyond imaginably vast universe, from the universe. God separates.
This principle of separation He uses from the beginning of creation through its end. He separates that which is not life or harmful to life from that which is life and sustains life.