And now, as we go on again into the third life, the outcome of the suffering which came to us (though only of that suffering which came, as it were, out of our own stored-up hatred), the outcome of the pain which was thus spent in our soul is a kind of mental dullness — dullness as compared with quick, open-minded insight into the world.
There may be a man who meets the world with a phlegmatic indifference. He does not confront the things of the world, or other men with an open heart. The fact is, very often, that he acquired this obtuseness of spirit by his sufferings in a former life on earth, the cause of which lay in his own karma. For the suffering which subsequently finds expression in this way, in dullness of soul, is sure to have been the result of feelings of hatred, at least in the last earthly life but one. You can be absolutely sure of it: stupidity in any one life is always the outcome of hatred in this or that preceding life.
Yet, my dear friends, the true concept of karma must not only be based on this; it is not only to enable us to understand life. No, we must also conceive it as an impulse in life. We must be conscious that there is not only an a b c d, but an e f g h. That is to say, there are the coming earthly lives and what we develop as the content of our soul in this life will have its outcome and effect in the next life. If anyone wants to be extra stupid in his next earthly life but one, he need only hate very much in this life. But the converse is also true: if he wants to have free and open insight in the next earthly life but one, he need only love extra much in this life.
Source: Rudolf Steiner – GA 235 – Karmic Relationships: Esoteric Studies – Volume I: Lecture IV – Dornach, 24th February 1924
Translated by G. Adams, M. Cotterell, C. Davy, & D. S. Osmond