The Bible was divided into chapters in the 13th century, and thus regardless of one’s view of the Bible, there is no need to take the existing divisions as an authoritative division of the text. And in fact there is a mistake in the very first such division, since the first part of Genesis 2 clearly belongs with the first chapter:

Thus the heavens and the earth were finished, and all their multitude. And on the seventh day God finished the work that he had done, and he rested on the seventh day from all the work that he had done. So God blessed the seventh day and hallowed it, because on it God rested from all the work that he had done in creation.

These are the generations of the heavens and the earth when they were created.

The text has a structure which marks the six days off from one another. Thus we have:

1:5-6 And there was evening and there was morning, the first day. And God said, “Let there be a dome…”

1:8-9 And there was evening and there was morning, the second day. And God said, “Let the waters…”

1:13-14 And there was evening and there was morning, the third day. And God said, “Let there be lights…”

1:19-20 And there was evening and there was morning, the fourth day. And God said, “Let the waters…”

1:23-24 And there was evening and there was morning, the fifth day. And God said, “Let the earth…”

1:31 And there was evening and there was morning, the sixth day.

After the sixth day, there follows the passage quoted above at the beginning of chapter 2. Thus, each day ends with “there was evening and there was morning,” except for the seventh day. And likewise, each day begins with “And God said,” except for the seventh day, presumably because on each of the other days, God does some work, but on the seventh day, he rests.

This structure tells us when the first day begins. The first day begins in 1:3, where you have “Then God said, ‘Let there be light’; and there was light.” This is a bit odd, because it leaves something before the first day:

In the beginning when God created the heavens and the earth, the earth was a formless void and darkness covered the face of the deep, while a wind from God swept over the face of the waters.

This is traditionally read as “In the beginning God created the heavens and the earth,” but the NRSV, used here, reads it as “when God created the heavens and the earth.”

This can be understood better by considering what things are created during these six days. When 2:1 says, “Thus the heavens and the earth were finished, and all their multitude,” the distinction between “the heavens and the earth,” and “all their multitude” is not an accidental one, but refers to different things created during the six days. The “heavens and the earth” refers to the first three days, and “all their multitude” to the second period of three days. Consider what happens during each of the days:

1. The first day: Light is separated from darkness.
2. The second day: Waters above the dome are separated from waters below the dome.
3. The third day: Water is separated from dry land, and vegetation is created.
4. The fourth day: Day is separated from night with the creation of lights in the sky.
5. The fifth day: The water is filled with sea creatures, and the sky with birds.
6. The sixth day: The dry land is filled with animals and human beings.

Basically the “heavens and the earth” are built, top down, during the first three days, and then they are filled with “all their multitude,” in the same fashion, from top to bottom. Vegetation is included on the third day because it does not move, and thus seems part of the dry land, while the lights in the sky, the sea creatures, birds, animals and human beings are all moving things.

The fact that something happens before the first day indicates that this order is not a temporal order, since otherwise there obviously could be nothing before the beginning of time. So what kind of order is it? We can see this from several things. Throughout the first four days, God is said to create by separating one thing from another, and before the first day, the earth is said to be a “formless void.” And during the fourth through sixth days, the stable foundation of the “heavens and the earth” are filled with moving things.

The order here is of material causality. Thus something confused (not yet distinct) may be matter for distinct things which are formed from it, and likewise the moving things in the world are like form relative to the “heavens and the earth”, which are like matter. This also explains why God says “Let the waters bring forth,” and “Let the earth bring forth,” when he creates the animals, fish, and birds. For these things are literally formed from the matter of the earth and the seas.

Thus the days represent the acts in which God imposes form on matter. And thus the earth is a “formless void” before the first day, because no form has yet been imposed. St. Augustine interprets the text in a similar way (The Literal Meaning of Genesis, book 1, chapters 3-4):

Why, moreover, is it stated, In the beginning God created heaven and earth, and not, “In the beginning God said, ‘Let there be heaven and earth,’ and heaven and earth were made”? For in the case of light, the words are: God said, “Let there be light,” and light was made. Are we to understand that by the expression, heaven and earth, all that God made is to be included and brought to mind first in a general way, and that then the manner of creation is to be worked out in detail, as for each object the words God said occur? For whatever God made He made through His Word.

But perhaps there is another reason why the expression, God said, “Let there be…,” could not be used in reference to the creation of formless matter, whether spiritual or material. God in His eternity says all through His Word, not by the sound of a voice, nor by a thinking process that measures out its speech, but by the light of Divine Wisdom, coeternal with Himself and born of Himself. Now an imperfect being which, in contrast to the Supreme Being and First Cause, tends to nothingness because of its formless state, does not imitate the exemplar in the Word, who is inseparably united to the Father. But it does imitate the exemplar in the Word, who exists forever in immutable union with the Father, when in view of its own appropriate conversion to the true and eternal Being, namely, the Creator of its own substance, it also receives its proper form and becomes a perfect creature.

Some people might say that it is not possible that the book of Genesis would refer to a philosophical idea such as prime matter, but this simply indicates that they are making things too complicated themselves. Causality always implies a first cause, and this is true in the order of material causality just as in other causes. Thus the author of Genesis is simply presenting the four causes of the world: the efficient cause, God; the material cause, the “formless void,”; the formal cause, the distinction and order of parts by which the world is formed; and the final cause, when he says, “God saw everything that he had made, and indeed, it was very good.”