If you want to have a real concept of the truths of the spiritual world, you have to distinguish reality and truth. You get to know a new world, but getting to know and judging is not the same, it is very different. You can experience many things in the spiritual world, you can be able to tell many things of it; the things that you tell can be real pictures, you may have beheld the picture properly — however, it has not to be true. As paradoxical as it sounds, I have to say that it is something extremely important that someone who wants to enter into this spiritual world brings the judgement from the usual world with him.
Somebody who has learnt to develop common sense in the usual world who does not deceive himself and is not deceived by anything in the usual world will bring common sense with him into the spiritual world and will judge the things that he beholds there correctly. Only by own judgement, reality becomes truth. You cannot develop judgement in the spiritual world; you have to bring it with you. One is allowed to say, someone who thinks logically in the usual world will also find the right and the true in the spiritual world. He who is a fool in the usual world and thinks illogically will think even more brainlessly and illogically if he applies his thinking to the things of the spiritual world. The most necessary if the human being wants to make a decision of truth or error in the spiritual world is the development of a healthy sense of truth and a healthy talent for observing in the physical world. You should not trust in someone who does not note with attention, with healthy talent for observation how the things proceed in the physical world and who proceeds inexactly in the physical world, if he tells anything of the spiritual world. Since the things of the spiritual world become true only if they touch our sense of truth.
A certain moral sense and spiritual condition is also necessary. Someone who enters into the spiritual world with a moral spiritual condition will come into relation with the healthy forces of the spiritual world and get to know its truths. However, someone who enters with immoral forces, in particular not with a meticulous sense of truth beholds everything distorted, caricatured in the spiritual world and, hence, tells it this way.
Source: Rudolf Steiner – GA 69a – Truths of Spiritual Research – Munich, 25 November 1912