Thinking normally is a mere appearance without any substance. Thinking always has a content - thought - but we grasp through it. We could 'stumble at' thoughts, because they are untrue or unsympathetic, but we will not get any bruises from them. Thoughts are without any force or strength; they don't bear much light either, because thoughts are obscure - although they bring light, in a way, whenever they lead to insight.
Through thinking-exercises, our thinking achieves another shape and effect. The more effort the thinker takes to understand certain thoughts and think them over and over, or to concentrate the mind on certain thought-complexes, the more thinking becomes a shaping force or power. At first it was only image, now it begins to work, and the force is an understanding force, it enlightens. It is no imagined force anymore, but a true activity of thinking, in which content is less important than force. We can renounce the content and turn the mind to the thinking activity, the force. This thinking of thinking remains full of notion, it is comprehensive. It will never be a dumb empty force, for it is seeking the concept itself that has become this force. Without any content it remains a self-understanding thinking.
However, thinking would never become force, had it not have been brought to activity by the thinker, with will. It also has to be initiated continuously. The thinking-activity becomes activity of will, and the thinker discovers that it is the initiative of the will that transforms thinking from image into force. But while it retains its image nature, it becomes imaginative force, 'Bildekraft".
In this moment the thinker knows that something exists that is not physical and yet still really exists and is self-conscious too. If we didn't have a name for it yet, we could call it “imaginative shaping thinking force”. But we do have a name: etheric body.
When this thinking and willing reality is there, we can actually perceive it with the same willing thinking. We are in a condition in which we normally never are. It is a truly exceptional state (Ausnahmezustand). We are in a position that is beyond normal consciousness, with a new 'working' consciousness.
This is the first perception of our own real Spirit.
It is the foundation of anthroposophy as movement of the spirit.