The astral plane and devachanic plane are in fact densely populated worlds. We find many kinds of beings there whose effects are manifested here on the physical plane though not obviously, and who have much to do with the physical plane, with our whole modern human life. One does not understand this life if one does not know that beings who live above in higher worlds are active within it. In the human body itself much goes on over which man is not master, which is not the expression of the human ego but the deed, effect, manifestation, of beings of higher worlds.
Source: Rudolf Steiner – GA 102 – The Influence of Spiritual Beings on Man: Lecture I – Berlin, 6th January 1908