In the first few pages they make an interesting observation. Actually, they make the observation in their very first sentence, but it took a couple of pages before I understood its significance:
Although the entire physical universe may be the object of investigation by the natural sciences, not all of its attributes fall within the domain of scientific inquiry.
What does this mean?
The authors attempt to illustrate the distinction by suggesting how we might study a page in a book.
Suppose we were able to describe every aspect of the page from the perspective of a natural scientist. Suppose we analyzed its chemical and physical characteristics, the distribution of atoms, the specific locations of different compounds, the proportions and dimensions and spatial relations of all the physical
At the end of such an analysis, would we have missed anything of significance?
No amount of scientific investigation--at least no amount of scientific inquiry of the type described here--could possibly reveal, 1) that the object of our study [what we--as observers--know is a page of the book] actually is intended to convey meaning, or 2) what that meaning really is.
And, thus, "to say that this page is nothing but a particular assembly of atoms and molecules, or to assert that the physical universe is 'all that is or ever was or ever will be' (as Carl Sagan does in Cosmos, p. 1) is to speak nonsense."