The route of the road to Treegap was developed long ago by a herd of cows. The road meanders pleasantly over and around hills and meadows until it gets to the wood, at which point it makes a sharp turn to go around the wood. On the other side of the wood, the road loses its pleasantness as it leads into the village of Treegap. It becomes straight and the grasses on either side look sad. The first cottage it passes has an iron fence around a cropped lawn, and it looks imposing and cold. The narrator says that this cottage, the jailhouse, and the gallows are the only things in Treegap that matter to the story.
Notice that the narrator's true interest is in the natural world surrounding Treegap, not the village of Treegap itself. By drawing a contrast between the wilder landscape outside of Treegap and the cut lawn on the inside of the cottage's fence, the narrator also shows how people have the ability to manipulate the natural world and make it look the way they want it to--though the language suggests that this isn't necessarily a good choice.
The narrator says the wood is strange. Both the first cottage and the wood make a person want to pass by without disturbing them, but for different reasons. The wood looks like it's sleeping and shouldn't be disturbed, and the Fosters, the family that own the imposing cottage, also own the wood. The narrator suggests that the idea of owning land is odd, as it's unclear whether a person owns just the top of the earth or whether ownership extends all the way to the earth's core. Even though the Fosters own the wood, none of them, even the 10-year-old child Winnie, goes there. Winnie's not even curious about it, which the narrator suggests is because her family owns it and things are only interesting when they're not your own.
When the narrator insists that the idea of owning land is an odd one, it suggests that the narrator would advocate for a relationship to land that isn't predicated on ownership and instead would be based on a sense of curiosity and community. This shows that as far as the narrator is concerned, humans are an intrinsic part of the natural world, even as they try to impose unnatural systems of ownership on it.
While the wood itself may be just like any other wood, with trees, birds, leaves, and bugs, the narrator suggests that the cows that routed the road around the wood were very wise. Had the road led through the wood, the people would've gone through too. Then, the people would've noticed a giant ash tree and a spring coming from around its roots, though the spring is hidden under a pile of pebbles. The narrator says that this would be a disaster that would make the whole planet tremble.
Here, by telling the reader outright that discovering the spring would be a disaster, the narrator shows that there are certain parts of the natural world that definitely shouldn't be owned or even known about. By giving credit to the cows for keeping this disaster from taking place, the narrator also indicates that all choices, no matter how they're made or how innocuous they seem, have major consequences.