Evil has to exist so as to strengthen the forces of the human being

One needs to be aware that the evil powers should also be incorporated into earth development. During the time in which these powers must then be overcome again, human beings will have to exercise great strength to transform the evil and demonic again into the good. But his strength will thereby grow, because evil is there to strengthen the power of the human being through his victory over it. All evil must be melted down and transformed into the good again, and it is so placed by providence in order to develop strong activity in mankind, much stronger than if he never should have had to transform evil into good.

Source (German): Rudolf Steiner – GA 101 –  Mythen und Sagen, Okkulte Zeichen und Symbole – Cologne, 28 December 1907 (p 237-238)

Translated by Nesta Carsten-Krüger