What is material and what is not? When the world is the end and God is the means to attain that end, that is material. When God is the end and the world is only the means to attain that end, spirituality has begun.
What do you want to do sadhana for? The aim should not be the satisfaction of egoism: "I want to be a great yogi; I shall have so much power and with that power I shall establish myself in the world." All such thoughts must be thrown far away.
How I understand the philosopher - as a terrible explosive, endangering everthing... my concept of the philosopher is worlds removed from any concept that would include even a Kant, not to speak of academic "ruminants" and other professors of philosophy.
Become aware of internal, subjective, subverbal experiences, so that these experiences can be brought into the world of abstraction, of conversation, of naming, etc. with the consequence that it immediately becomes possible for a certain amount of control to be exerted over these hitherto unconscious and uncontrollable processes.