What does Genesis 1:6 mean?

Genesis chapter 1 follows a rigid structure, according to a very specific pattern. God will create something through His words, observe it, declare it good, and then Scripture will indicate the number of that creative day. The first half of these moments—days one, two, and three—prepare creation for some future component. The corresponding days in the second half—days four, five, and six—show the creation of that new thing.

In the prior verses, God completed the first day of creation, making light, day, and night. Here, God turns to the waters. Verse 2 indicated that the earth was formless, void, and covered by deep waters. Now God issues a command about those waters: separate them.

More specifically, God calls for something to be placed between the waters: a space or firmament or vault or sky or heaven (depending on the translation). The Hebrew term is rā'qi'a, which implies something solid and supportive. The word-picture offered here seems to be of raising up the top part of the waters and inserting an open area: what we would usually think of as the "air" above the sea or land.

But what about the top layer, the "waters" above the sky? Some scholars suggest those are the clouds of the upper atmosphere or simply the atmosphere itself. Others have speculated that a water "canopy" once existed in the upper atmosphere that is no longer there in our day. In any case, the larger point of the verse is that God's power includes the ability to order even the oceans to do His bidding and breathable air to come into existence on the earth. Once again, God and God alone is credited with creating the world as we know it.