When we refer to the will, we are dealing with that which makes us of value to the world, which so places us in the world that we not only live a life of knowledge and a life of feeling within ourselves, but are able to re-act upon the world. What a human being wills, and what flows from his will into his actions, constitutes his value to the world.
Thus we may say that in referring to the realm of will we are dealing with that element which shows that man is a part of the world and it is our inner life which thus flows out into the world and forms part of it. Whether they are the emotions and passions of criminal natures hostile to social life that flow into the will and thence become part of the world to the world’s detriment, or whether they are the high, pure ideals which the idealist draws down from his contact with the spiritual ordering of the world and allows to flow into his actions, allows to flow perhaps only into his words which act upon human beings, stimulating them or revealing the worth of man — in either case we are always dealing with what lies in the realm of will, with what gives to man his value.
So that all the wealth which man can really possess as a soul-being, is expressed, when we mention these four realms: Perceptions, Thought, Feeling and Will.
Source: Rudolf Steiner – GA 153 – The Inner Nature of Man and Life Between Death and Rebirth: Lecture 1 – Vienna, 9th April, 1914