Our contemporaries do not want to get involved in these higher worlds. Our age is tired of the consideration of the supersensible world, and, hence, this age is very gullible toward those who put up the sentence: what I cannot perceive is not true, and if anybody asserts, it is true, he is a poor devil or a fool. — Too many people become believers of such an opinion in this age. Even if we also realise which big and immense progress our age has performed concerning the physical science, nevertheless, we also see on the other side how little the predominating part of our contemporaries is inclined to penetrate into the supersensible world. One means that the penetration in the supersensible world makes the human being weak and foreign towards the sensuous world. This is a prejudice. If anybody has a piece of iron and says: this iron has magnetic force; touch it with another iron and you have a magnet — another may come and say, nonsense! The piece of iron is good for hammering down nails. — These are the true daydreamers who take the sensuous, the practical only in such a way as that man who hammers down nails only with the magnet.
The realists, the monists, the utilitarians, and others are the true daydreamers. They know the forces of the physical world only and triumph if the immense progress is done by merely revealing the forces of the physical world. Spiritual science has to argue nothing at all against this physical world. However, it also knows that it is high time that the human beings learn again that in the physical the spiritual is concealed, and that just the human beings become dreamy when they close their spiritual eye to the spiritual world. Today true realists, apostles of reality are those who point to the spiritual forces! What do these truthful realists want? They want that the real forces slumbering behind the sensuous are introduced in this world that they settle down in our whole development that we do not only introduce the telegraph, the telephone and the railway, the usual forces but also the spiritual forces.
Source: Rudolf Steiner – GA 56 – Knowledge of Soul and Spirit: Lecture XV: The Heaven – Berlin, 14 May 1908