Any life that is taken away from a living being, any harm that is caused to a living being lessens the noblest forces of our own human nature because of a connection which exists between life and life. Just as a quantity of mechanical work can be transformed into heat, something changes by the homicide of a living being in the human being, so that he becomes unable to have an curative and beneficial effect on his fellow men. This is an unbreakable principle. Here everything nebulous, everything unclear is strictly impossible. Here rules mathematical clarity.
Source: Rudolf Steiner – GA 53 – Origin and Goal of the Human Being – Lecture XXII – Berlin, 25th May 1905