In the present age, Ahriman can only have a strong influence upon men when their consciousness is diverted in one way or another. The most radical phenomenon is that of a fainting fit, or a diminution of consciousness lasting for a considerable time. In times like this, when a man is overcome by faintness or diminution of consciousness, the Ahriman forces can most effectively approach him. At such times they work their way into him, he is exposed to them. [….]
Needless to say, Spirits like Ahriman are not there to incarnate in physical bodies on the earth. Nevertheless, they can work on the earth, not indeed by incarnating but by incorporating themselves for certain spaces of time; when in one man or another there happens what I mentioned before: a diminution or diversion of consciousness. At such moments the human being provides a vehicle, and Ahriman is able — not indeed to incarnate, — but to incorporate himself and to work out of that human being, with that human being’s faculties.
It will be my further task to tell you of this kind of working of the Ahrimanic Powers. I shall have to show, for example, how Ahriman has appeared in the course of modern time even as an author. This will show you what things must be observed today by those who would fain observe realities.
Source: Rudolf Steiner – GA 237 – Karmic Relationships / Esoteric Studies III – Lecture 9: Entry of the Michael Forces – Dornach, August 3rd, 1924
Translated by George Adams, with revisions by D. S. Osmond