If the raising of man is actually to occur, then the experiences we have with the physical world must lead us over into the spiritual world. […] Whoever has not accustomed himself to remaining with the facts in the physical sense world and to basing himself upon them also does not accustom himself to truthfulness when speaking about the spirit. For in the spiritual world, one can no longer accustom oneself to truthfulness; one must bring it with one.
Source: Rudolf Steiner – GA 220 – Fall and Redemption – Dornach, 21st January 1923
The great Rudolf Steiner Quotes Site 