You will understand the physical world, only if you learn to know the spiritual world. Spiritual science is not meant for cranks, but for the most practical of the practical! Every form of life is spiritual. Even as ice is condensed water, so matter is condensed spirit. Mineral, plant, animal, or man — each is a condensed form of the spirit.
Source: Rudolf Steiner – GA 100 – Theosophy and Rosicrucianism: Lecture I – Kassel, 16th June 1907