Rudolf Steiner:
4. For certainty of feeling and for a strong unfolding of his will, man needs a knowledge of the spiritual world. However widely he may feel the greatness, beauty, and wisdom of the natural world, this world gives him no answer to the question of his own being. His own being holds together the materials and forces of the natural world in the living and sensitive form of man until the moment when he passes through the gate of death. Then Nature receives this human form, and Nature cannot hold it together; she can but dissolve and disperse it. Great, beautiful, wisdom-filled Nature does indeed answer the question, How is the human form dissolved and destroyed? but not the other question, How is it maintained and held together? No theoretical objection can dispel this question from the feeling soul of man, unless indeed he prefers to lull himself to sleep. The presence of this question must incessantly maintain alive, in every human soul that is really awake, the longing for spiritual paths of World-knowledge.
5. For peace in his inner life, man needs Self-knowledge in the Spirit. He finds himself in his Thinking, Feeling, and Willing. He sees how Thinking, Feeling, and Willing are dependent on the natural man. In all their developments, they must follow the health and sickness, the strengthening and weakening of the body. Every sleep blots them out. Thus the experience of everyday life shows the spiritual consciousness of man in the greatest imaginable dependence on his bodily existence. Man suddenly becomes aware that in this realm of ordinary experience Self-knowledge may be utterly lost — the search for it a vain quest. Then first the anxious question arises: Can there be a Self-knowledge transcending the ordinary experiences of life? Can we have any certainty at all, as to a true Self of man? Anthroposophy would fain answer this question on a firm basis of spiritual experience. In so doing it takes its stand, not on any opinion or belief, but on a conscious experience in the Spirit — an experience in its own nature no less certain than the conscious experience in the body.