In the thirteenth century spiritual darkness fell for a time upon all human beings, even the most enlightened, and also upon the initiates. Whatever knowledge of the spiritual worlds existed in the thirteenth century came from tradition or from men who in still earlier times had been initiates and were able to call up memories of what they had then experienced. But for a brief space of time it was impossible even for these men to have direct vision of the spiritual world. Darkness had to fall for this short period to prepare for the intellectual culture which was to be characteristic of our modern age. The important point is that we have this kind of culture today in the fifth post-Atlantean epoch. Culture in the Greek epoch was quite different. Instead of the modern, intellectual kind of thinking, direct perception was then the dominant faculty; the human being was one, as it were, with what he saw and heard, even with what he thought. He did not cogitate and reason as he does today, and needs must do, for this is the task of the fifth post-Atlantean epoch. In the thirteenth century it was necessary for especially suitable personalities to be singled out for initiation, and the initiation itself could only take place after that brief period of darkness had come to an end.
Source: Rudolf Steiner – GA 130 – Esoteric Christianity and the Mission of Christian Rosenkreutz – Lecture 1 – Cassel, 27th January 1912