Rudolf Steiner, from a lecture given April 18, 1909:
...the essential thing in Christianity is the deed which can become one's own possession only through free will, through a voluntary ascent into the higher worlds. Man takes the Christ-force into himself because he voluntarily receives it, and no one can receive it who does not do so voluntarily. This has only been made possible for man because he has become human upon Earth, because he was called to grow into man on Earth.
The fallen Angels who have spread over the Earth as Lucifer are in a different position. These ought really to have become men on the Moon; they have remained behind in their development, hence they can enter the astral body but not the ego. They are in a peculiar position, a position which we can only describe graphically, even if it appears somewhat pedantic. Let us suppose, leaving aside the physical and etheric body, that the astral body of man during the Lemurian development was represented by the circle A-B-C, and the ego was the circle enclosed (a) in that astral body. The Ego gradually entered the astral body. What happens now? During the Lemurian development the Luciferic forces slip on all sides into the man's astral body and penetrate him with their activities, which find expression in his lower passions. That through which he succumbs to error and evil is rooted in his astral body; the Luciferic spirits have implanted this into him. (If they had not done this he would never have had the possibility of error and evil, he would have been lifted up to the place from which he receives his ego, untouched by all hindering influences.) So it goes on, but the great leaders protect humanity as far as it is necessary so that it should not sink too low.
Now comes the Advent of the Christ. Let us take a man who has voluntarily received the Christ. Christianity is only at its beginning. But let us take the Ideal; the man's ego has voluntarily, with complete free will, allowed the Christ's force to flow into him. When the ego has progressed so far that it has filled itself with the Christ, then this Christ force irradiates the astral body also. In that same astral body into which the Luciferic powers had formerly implanted their deeds, the Christ power is now radiating from within outwards. What happens in the future? Because we have overcome with the help of Christ, and only with His help, all those human qualities which come from Lucifer, we also, as men, gradually release the Luciferic powers; and a time will come when the Luciferic powers who, during the Moon development, had to sink downwards into a certain lower evolution for the sake of human freedom, and who had not themselves the opportunity of experiencing the Christ force upon Earth, these Luciferic powers will experience the Christ force through man, and through Him they will be released. Man will save Lucifer when man takes the Christ force into himself in the necessary way. And because of this, man will again grow stronger than he otherwise would have been. For imagine: if man had not received the Luciferic powers, then the Christ force irradiating him would not have encountered the hindrances of the Luciferic forces, and it would have been impossible for man to progress so far in wisdom, goodness, and truth as he may do when he has to overcome these opposing forces....