And God said,
Let there be a firmament in the midst of the waters, and let it divide the waters from the waters.
All Commentaries on Genesis 1:6 Go To Genesis 1
Ephrem The Syrian
The waters that the earth drank on the first day were not salty. Even if they were like the deep on the surface of the earth, they were still not seas. For it was in the seas that these waters, which were not salty before being gathered together, became salty. When they were sent throughout the entire earth for the earth to drink they were sweet, but when they were gathered into seas on the third day, they became salty, lest they become stagnant due to their being gathered together and so that they might receive the rivers that enter into them without increasing. For the quantity that the seas require for nourishment is the measure of the rivers that flow down into them. The rivers flow down into the seas lest the heat of the sun dry them up. The saltiness [ of the seas ] then swallows up [ the rivers ] lest they increase, rise up and cover the earth. Thus the rivers turn into nothing, as it were, because the saltiness of the sea swallows them up.
Even if the seas were created when the waters were created and were hidden in the waters, and the seas were bitter, the waters above them were not bitter. For just as in the flood there were seas, but they were covered over [ by those waters ], they were not able to change the sweet waters of the flood, which came from above, into their bitter nature, for if these waters had been bitter, how were the olives and all the plants preserved in them? How did those of the house of Noah and those with them drink from them?
Even if Noah had commanded that every food be brought for himself and those with him because there would be no food anywhere, he did not allow water to be brought because those who had entered the ark would be able to take the water from outside of the ark to drink. Therefore, just as the waters of the flood were not salty while the seas were hidden within them, neither were the waters that were gathered on the third day bitter even though the seas below them were bitter.
Just as the gathering of the waters did not precede that word which said, "Let the waters be gathered and let the dry land appear," [ Gen1:9 ] neither did the seas exist until that moment when God "called the gathering of water 'seas'." When they received their name they were changed. In their [ new ] place the [ waters ] attained that saltiness which had not been theirs [ even ] outside of their [ old ] place. For their place became deep at that very moment when God said, "Let the waters be gathered into one place." [ Gen1:9 ] Then either the land [ that contained ] the sea was brought down below the [ level of the ] earth to receive within it its own waters along with the waters that were above the entire earth, or the waters swallowed each other so that the place might be sufficient for them, or the place of the sea shook and it became a great depth and the waters quickly hastened into that basin. Although the will of God had gathered these waters, when the earth was created, a gate was opened for them to be gathered into one place. Just as in the gathering of the first and second waters there was found no gathering place because there was no place from which they might go out, so now do these waters come down with all the rains and showers and are gathered into seas along paths and roads which had been prepared for them on the first day.
After Moses spoke of those things that came to be on the first day, he began to write about those things that came to be on the second day, saying, "And God said, 'Let there be a firmament between the waters and let it separate the waters below the firmament from the waters above the firmament.'" [ Gen1:6 ] The firmament between the waters was pressed together from the waters. It was of the same measure as the waters that were spread out over the surface of the earth. Then if, in its origin, it was above the earth (for the earth, water and fire were beneath it, while water, wind and darkness were above it), how do others posit that this [ firmament ], which encloses this world within it like a child in the womb, was created in the middle of everything as the womb of everything?
If, on the other hand, the firmament had been created as the center of everything, light, darkness and wind, which were above the firmament when it was created, would have been confined above the firmament. If the creation [ of the firmament ] had occurred at night, the darkness and wind would also have remained there together with the waters which remained there. But if the creation [ of the firmament ] had occurred in the day, the light and the wind also would have remained there along with the waters. And if the [ wind, water and lights ] had remained there then the [ wind, water and lights ] here would be other things. When, then, could the [ wind, water and lights ] have been created? If, however, they did not remain there, how did those elements that were above [ the firmament ] when they were created move below it?