The first verse of Genesis 1, that grand opening statement, can be interpreted in a number of different ways.
In the beginning God created the heavens and the earth.
Some commentators see this as being a pre-creation that occurred before the actions of the following verses but Walton disagrees. Of the term 'beginning' he says (p45):
In Hebrew usage this adverb typically introduces a period of time rather than a point in time. We can see this most easily in Job 8:7
which says...
Your beginnings will seem humble, so prosperous will your future be.
So what Walton is suggesting is that verse 1 is actually referring to the period of the creation that follows in the rest of the chapter.
This suggests that verse 1 serves as a literary introduction to the rest of the chapter. This suggestion is confirmed by the fact that Genesis 2:1 concludes the seven-day report with the statement that the "heavens and earth were completed"