The central distinction that Walton makes is a distinction between "material existence" and "functional existence." Material existence focuses on physical matter; existence is defined as having certain physical properties. Functional existence, on the other hand, focuses on having a function in an ordered system; existence is defined as functioning properly in that ordered system.
Walton makes the point that when the contemporary world thinks about existence, we think about it in material terms. So when the Bible talks about God creating the sun, we imagine that there's nothing material there and then "poof!" there it is (okay, maybe that's the Sunday School version, but it's still the version many people imagine). Functional existence, on the other hand, asks why matter matters: what it is for and what does it do?
One of Walton's key points is that creation stories of the Ancient Near East do not have a material focus, but a functional focus. Part of the reason that Genesis 1 doesn't make sense to us is because we assume a "material" lens, when the ANE creation stories, including Genesis 1, should be seen through a "functional" one.
So where does Walton get this distinction? How does it emerge in the text? One way is through considering the "formless and void" of Gen. 1:2. If Gen. 1:1 is the literary heading to the story (in other words, "this is the story of how God created the heavens and the earth") and not a single or separate act of creation, then the creation narrative simply jumps right in with 1:2, assuming "darkness on the face of the deep" and the wind/Spirit "hovering over the waters." In other words, it talks like there's already something there materially but not functionally. If we focus on material existence, Gen. 1:2 poses a big problem: there's already stuff here! But if we focus on functional existence, the problem vanishes: the text isn't about material stuff per se but about God giving form and function to what's already there. Walton points out that the Hebrew term tohu, which is used in Gen. 1:2, appears elsewhere in the Old Testament. For example, it can reference a wasteland/wilderness (Deut. 32:10, Job 6:18; 12:24; 107:40) and a ruined city (Is. 24:10). The wilderness certainly exists in a material sense, but not in a functional one. The wilderness is not a garden. Likewise, the ruined city is desolate. It's still there materially but not functionally. So that's one piece of the puzzle: the issue in Gen. 1:2 is not that there are no material things but that creation needs purpose and function.
Scholars have often noted that days 1-3 are the "forming" and days 4-6 are the "filling" of what God has made. Walton, I think, would affirm that, but he talks about days 1-3 in terms of function. God creates light and calls the light "day" and the darkness "night." In other words, when the text says God created "light" it means "period of light." But a "period of light" is not a material thing. So, argues Walton, the focus is not on the material reality of light per se but on the basic function of time: day and night. Likewise, in day 2 God doesn't create waters in the material sense. He doesn't say "let there be water!" The text just assumes the waters are already there. Instead, God divides the waters above from the waters below. Likewise, on day 3, God doesn't say "let there be land!" Rather, God gathers the waters together so that the dry ground will appear (God does this post-flood in Genesis 8 as well). So Walton argues that days 2 and 3 explain the basic functions of weather and food.
One main analogy that Walton uses to clarify the material vs. functional distinction is that of house vs. home. The house must materially exist, but it doesn't make a home. Only when someone sets it up to be functional for their life and family is it ready to be lived in. According to Walton, Genesis 1 is the home story, not the house story. In our scientifically-minded culture, we want and expect the house story. But what if that's not what the Bible is telling us? Then we might have to re-think our expectations.
So what if the focus of Genesis 1 is functional and not material? Here's where Walton sounds controversial to some (and late on the scene to others). If the creation story in the Bible is functional and not material, then the Bible doesn't have a material story of origins that has to be defended over against other views. Is God the material Creator of all things? Of course. But Genesis 1 is not the house story, it's the home story. Genesis 1 explains why matter matters, but it's not trying to chart any kind of scientific timeline. Another biblical analogy helps here: Solomon's Temple is constructed over a period of 7 years, but dedicated over the course of 7 days (Walton's book also explores the Temple connection with Genesis 1). But when does the temple become the temple? The material construction of the temple is not what makes the temple what it is. It becomes the temple in the 7-day celebration in which the glory of God rests in it (see also: 7th day of creation). The temple exists materially for a long time before it exists functionally. That is, before the ministry of the priests in the Temple actually begins and the regular functioning of the temple commences. In light of this analogy, Walton sees no problem in affirming that Genesis 1 as talking about 7 actual solar days. But these are not days of material creation but of functional creation.
One final analogy (mine, not Walton's): the extra features on the Lord of the Rings DVD's show all the background work that went into creating those movies. It's interesting to watch the time, effort, and energy that went into setting the stage. But those extras aren't the actual story. They serve the story, but no one would mistake the extra features for the story itself. If Walton is right, then many Christians are reading Genesis 1 as the "extra features" rather than as the story itself. If Walton is right, God has the pieces of the puzzle set in place; the background is set and the actors are about to come on the stage. Genesis 1 is God's version of "lights, camera, action!" As Creator and Sustainer, God thus initiates and inaugurates this great cosmic drama that's about to unfold. Or in the words of Shakespeare, "The play's the thing!"
Obviously a short blog post like this can only barely scratch the surface of Genesis 1. But I hope that this gives some food for thought as we think about what God is communicating through Scripture.