And anyone who declares that ordinary knowledge acquired through healthy human reason does not give him eyes for supersensible existence but that for this he needs clairvoyance — anyone who speaks like this might just as well declare that man cannot think unless his eyes do the thinking. As little as in physical life the eyes need think, as little does knowledge of the supersensible worlds need clairvoyance for the purposes I have indicated today.
Naturally, there would be no supersensible knowledge on Earth if there were no clairvoyance; but even the seer must make intelligible in the ordinary way what he sees in the supersensible. However powerful a man’s clairvoyant faculty might be in earthly life, however clear his vision of the spiritual world, if he were too easy-going to bring into the form of logical, intelligible ideas what he sees in the spiritual world, he would still be blinded in the spiritual world after death.
What constitutes the great suffering for one who has insight into modern Initiation-Science is that he must admit: materialism makes men blind when they pass through the gate of death. And here again is something showing that it is of significance for the whole of cosmic existence whether man today inclines to supersensible knowledge or not. The time when it is essential for him to do so has arrived; the very progress of humanity depends upon man acquiring supersensible knowledge.
Source: Rudolf Steiner- GA 219 – Man/World of Stars: IV: Rhythms of Earthly and Spiritual Life. Love, Memory, the Moral Life. – Dornach, December 15, 1922