One of the questions asked most often in the beginning is: how do I know I have physical control over myself? The answer is simple: when you don't have to ask this question anymore, read: when you don't have to think about it anymore. That's when you've impressed your subconscious sufficiently enough to have this control rather than still doubting, still questioning.
This is also why it's so important to perhaps spend more than a week on each of the first four parts, but also - if not done already - engage in something like yoga, where it's part of the exercise to obtain physical control.
Here it is really only about sitting still, because the following 24 weeks you will be doing exactly that. In Chapter 2 you will learn how to gain control over your thoughts, and for that you will have to have control over your body, so this exercise is the foundation for all that is yet to come.
PS: Please also pay attention to the books or CDs I am recommending via links to Amazon. Whatever I am recommending here has been tried or read by myself. The musical work of Dr. Jeffrey Thompson deserves special attention, as it assists you in obtaining various mental states.