"If it were true, as the materialists maintain, that the brain does the thinking, then one could certainly give them some comfort. But this is as false as the assertion that the “speech-center” has formed itself. It has acquired its form through human beings having learnt to speak, and so the speech-center is the result of speech. Similarly, all cerebral activity, even in the historical past, is the result of thinking — not the other way about. The brain is plastically modeled through thinking. If only such thoughts are developed as are customary today, if the thoughts are not permeated by the wisdom of the spirit, then the souls occupied with thinking only about material things will find in later incarnations that they are unable to use their brains properly; their brain-forces will be too weak to lay hold of things. A soul which today is occupied merely with calculating debit and credit, let us say, or with the usages of commercial and industrial life, or absorbs only the ideas of materialistic science, is filling itself with thought-pictures which in later incarnations gradually darken the consciousness, because the brain would be an unformed mass — as today in cases of softening of the brain — and so no longer capable of being taken hold of by the forces of thinking. Hence for anyone who looks into these deeper forces of human evolution, everything that can live in the soul must be permeated by a spiritual comprehension of the world.
So in this modern time the nature of man may still be twofold. The forces belonging in particular to the Consciousness Soul must be infused with inner spiritual knowledge. Man must overcome the two regions through which Parsifal went; he must overcome “apathy and doubt” in his own soul. For if he were to carry apathy and doubt with him over to a later incarnation, he would not make a success of it. Man must come to have knowledge of the spiritual worlds. Only through the fact that life widens out in the human soul, the life called Saelde by Wolfram von Eschenbach, the very life that pours out spiritual knowledge over the Consciousness Soul — only by this means can human soul-development advance fruitfully from the fifth epoch onwards into the sixth."