Anger has its value for the development of the human being. The human being must purify himself, he must overcome anger. Anger is something that works beneficially in that it is overcome. The human being would never be able to reach perfection without conquering anger.
Source (German): Rudolf Steiner – GA 108 – Die Beantwortung von Welt- und Lebensfragen durch Anthroposophie – St. Gallen, November 21, 1909 (page 100)
Translated by Nesta Carsten-Krüger