Even if it were to be the case that everything we have taken up was wrong and the only thing we have done is to make an effort, this means we shall have developed the eye of the soul so that we are now able to see what it there in the spiritual world.
Now the situation is that the teachings of the different religious teachers are in no way completely wrong. It is rather that the truth concerning the supersensible world has been presented from different points of view and only appears to be contradictory. The one must be taken to complement the other. What is essential is that all these religious systems have something in common, and this is that they all provide the human soul with concepts the soul uses to make itself strong to enter the spiritual world, so that the soul is raised from death in its spiritual depths.
Individual religious teachers give to the souls what those souls are capable of receiving, depending on the conditions given in individual races — I would say depending on climatic conditions of the country and on the time when such teachers come forth. They all have in common that they give power and strength to the souls of men. We may also say they make them radiant within so that the souls may be real not only in the physical world but also in the spiritual world. Food to strengthen the soul is the universal truth that has been given to men in all religious systems, depending on the given situation.
Source: Rudolf Steiner – GA 157 – Destinies of Individuals and Nations: Lecture 6: Spiritual Perception Essential at the Present Time – Berlin, January 26, 1915