Where Nye's Second Creation is more of an academic retelling of history, Thoreau gives a different account of that history in his Walking. His work is more personalized. It is difficult to read his work because he jumps around so much; however, this style of writing goes very well with the message he is trying to convey.
Thoreau says that we need to experience nature while we can. Looking around today, there are not very many local forests to get lost in. The world has been explored, mapped out, and reorganized. Every day more nature is being destroyed to make room for homes, amusement parks, hotels, factories, etc. How many trees can one find in New York City? Thoreau is saying that while this reconstruction is not a completely horrible thing, we do need to treasure nature.
He talks about going on a walk just to see nature. While one is on this walk, they must just pay attention to nature. Forget about work, school, etc. This walk is just between the individual and nature. If the person's mind is constantly busy with other thoughts, then he is not giving nature the attention it deserves. The walk would be meaningless. Also, the walk should be pointless. The individual must not start from point A for the purpose of getting to point B. He should wander around, explore. Don't try to map everything out.
It seems as though Thoreau wants us to let go of the order mankind has created, and just go with the flow of nature, just for a time at least. Today not very many people do this. We start from point A and rush to point B missing everything in between. We miss the smells of flowers, the shapes of the clouds, the chirps of the birds, the soft glow of the moonlight, etc. We're too busy with out daily lives to notice these things that are not always going to be there. One day those flowers will die. The clouds will blow away. The birds will fly south. The moonlight will fade. In the end, all we could say is that we made good time on the freeway.