Just as there could be no life in the ordinary sense of the word without death, so can there be no true knowledge of the visible world without insight into the supersensible. All knowledge of what is visible must plunge again and again into the invisible in order to evolve. Thus it is evident that the science of the supersensible alone makes the life of revealed knowledge possible. It never weakens life when it appears in its true form. When, having been left to itself, life becomes weak and sickly, supersensible knowledge strengthens it and makes it, ever and again, fresh and healthy.
Source:Rudolf Steiner – GA 13 – An Outline of Occult Science – III. Sleep and Death
Translated by Maud and Henry B. Monges and revised for this edition by Lisa D. Monges.