This book contains some lectures by Rudolf Steiner that align with spiritual science (or "Grail Science").

The selection and composition of these lectures were made with the aim of addressing topics related to the anthroposophical approach to the human organism (and by extension, the anthroposophical approach to medicine) in relation to the suprasensory world.

The lectures begin with the fall of the spirits of darkness, continue with geographical medicine, the three stages of sleep, the formation of the etheric and astral heart, the spiritual relationships in the formation of the human organism, the properties of salt, mercury, and sulfur, the invisible human we have within us, the anthroposophical approach to medicine, the inner nature of music, and conclude with a lecture on polarities in health, disease, and healing.