This is an important book because it is a document written by Arnold Schoenberg. He wrote it from the way he taught his students harmony. If you know Schoenberg's tonal music you know how highly chromatic it is. It moves from tonal center to tonal center almost without the listener understanding how far they are traveling. This book uses his concept of region and that is not something taught in your freshman - sophomore theory courses.
If you want to read this book, make SURE you have a strong grounding in traditional theory first. Then ground yourself in Schoenberg's treatise on harmony. Then take on this little book. Otherwise it will be opaque to you.
However, just because you can't understand what the composer wrote, don't suppose that it is nonsense or dismiss it because of your own lack of comprehension. Schoenberg was a very important composer and understood the methods of composition very well. He certainly had his own views, however idiosyncratic they may be. It is simply that when you are Schoenberg you can do things lesser musicians cannot.