Knowledge of the healing forces is inseparable from knowledge of the forces of sickness. One cannot be taught without the other. No one in the world can gain knowledge of the healing forces, without at the same time learning about the forces of sickness. So you can see how important it is for people to be morally good through and through as regards such serious matters. For someone who can heal a person’s soul can also make a person’s soul sick in the same degree. Therefore such truths may not be imparted by the gods to man until a stage of morality has been reached at which the healing medicine cannot be transformed into poison.
Source: Rudolf Steiner – GA 173 – The Karma of Untruthfulness I: Lecture Nine – Dornach, 24th December 1916