You must realise that in the astral body and in the etheric body, as well as in the physical body, you feel the workings of other beings; all that you do involuntarily, everything to which you are impelled, is due to the working of other beings; it is not born from nothingness. The various members of man’s nature are all the time actually permeated and filled by other beings, and many of the exercises given by an initiated teacher are for the purpose of driving out these beings in order that a man may become more and more free.
The beings who permeate the astral body and make it unfree are known as “Demons.” Your astral body is always interpenetrated by demons and the beings you yourselves generate through your true or false thoughts are of such a nature that they gradually grow into demons. There are good demons, generated by good thoughts; but bad thoughts, above all those that are untruthful, generate demoniacal forms of the most terrible and frightful kind and these interlard the astral body — if I may so express it. The etheric body is also permeated by beings from which man must free himself; these beings are called “Spectres”, “ghosts.” And finally, permeating the physical body there are beings known as “Phantoms.”
Besides these three classes there are yet other beings, the “Spirits,” who drive the Ego hither and thither — the Ego itself also being a Spirit. In actual fact the human being generates such creatures who then determine his inner and outer destiny when he descends to incarnation. These beings work in your life in such a way that you can feel the “demons” created by your astral body, the “ghosts” or “spectres” created by your etheric body and the “phantoms” created by your physical body. All these beings are related to you and approach you when the time comes for reincarnation.
Source: Rudolf Steiner – GA 99 – Theosophy of the Rosicrucian: VI: THE LAW OF DESTINY – Munich, 30th May 1907
Translated by M. Cotterell & D.S. Osmond