The spiritual conception of the world is a curative conception. Many people will say in answer to this assertion: Are all Anthroposophists healthy people? Are there no invalids among them? We must understand that fundamentally the individual can do very little for his health and his sickness. A large proportion of the causes of disease lies outside the individual personality.
A person may have the healthiest ideas, which, if he were to live under quite healthy conditions, would result in his never being ill from internal causes; but there are other causes lying outside the power of the individual of today, the secret causes of heredity for example, the influences passing from one human being to another, the influences of unnatural environment, etc.
All these influences, which, in a hidden way, are external causes of disease, can only be done away with gradually by a healthy Anthroposophical method of thought. Although we may observe that a person who is inwardly most healthy may fall ill, even dangerously ill, we must not regard this as a sign that Spiritual Science will fail to act curatively upon humanity in the course of centuries — I say centuries, not thousands of years.
Source: Rudolf Steiner – GA 105 – Universe, Earth and Man: II – Stuttgart, 5th August, 1908