From Rudolf Steiner's the Gospel of St. John, p.174:

Catharsis is an ancient term for the purifying of the astral body by means of meditation and concentration exercises.  Catharsis, or purification, serves the purpose of ridding the astral body of any elements that keep it from being properly and harmoniously organized, so that higher organs can develop in it.  It is endowed with the potential for these higher organs; all one has to do is clear the way for the forces that are inherent in it. 

We spoke of the possibility of bringing about catharsis by a great variety of methods.  A person(s) have gone a long way toward achieving it if, for example, they have taken in and experienced the content of my Philosophy of Freedom with such inner participation that they have the feeling,” Yes, the book was a stimulus, but now I can reproduce the thoughts it contained by my own effort."  If a reader(s) takes the book as it was meant and relates to it in the way a virtuoso playing a composition on the piano relates to its composer, reproducing the whole piece out of themselves - in the composer's sense, naturally - the book's organically evolved thought sequence will bring about a high degree of catharsis in them.  For in the case of a book like PoF, the important thing is so to organize the thoughts it contains that they take effect.  With many other books it doesn't make a great deal of difference if one shifts the sequence, putting this thing first and that one later.  But in the case of The Philosophy of Freedom that is impossible.  It would be just as unthinkable to put page 150 fifty pages earlier as it would be to put a dog's hind legs where the front ones belong.  The book is a living organism, and to work one's way through the thoughts it contains is to undergo an inner training.  A person(s) to whom this has not happened as a result of their study need not conclude that what I am saying is incorrect, but rather that they have not read PoF correctly or worked hard and thoroughly enough.  ..........................

The above quote from Rudolf Steiner, for me, is a compelling picture of what can happen if one approaches PoF as a tool to train one's thinking.  The organic structure of PoF is like a symphony, in that following the thoughts and concepts as Steiner presents them to us therein, allows for an inner soul awakening that is one of (as stated in Steiner's quote) organized harmony.  Steiner has written PoF in such a way that if we follow it from beginning to end using our thinking and really working in our thinking to develop an understanding of what is being presented step by step, we can develop an inner soul experience of thinking that goes beyond our own limited ego.  Steiner speaks of PoF as a living organism and this is exactly what one may experience in one's inner life as one works with the book, something alive and evolving (not dead thoughts).  

PoF leading to a catharsis or purification of elements of the astral body -  to be experienced by the individual through their own effort.  If one thinks of the astral as reaching out into the cosmos, then through the right understanding and experience of PoF, one's thinking may evolve from the confinements of our lower ego out into the cosmic spheres in communion with our higher SELF.

Best regards to all,
Patri