How do human beings become still materialists?

Spiritual science acknowledges that behind everything, also behind the material existence, something spiritual works that the material existence is only the expression of spiritual forces working behind it. In the field where the material works, actually, the spirit is also effective.

How do human beings become still materialists? Why do they misjudge that — where matter appears — this matter is only the revelation of the spirit? If we recognise the spirit everywhere, we have also to look for the causes in the spirit, why human beings may become materialists. Indeed, these are spiritual reasons in the human soul, forces, which work from the spiritual world into this human soul that take the human being to a materialist attitude. Among those spiritual forces which spiritual research brings home to us, we find the so-called ahrimanic forces referring to the Persian spirit Ahriman. These are certain spiritual forces that have an effect on the human soul in such a way that they veil everything to him that does not appear in dense materiality. 

It is true what Goethe and all those say who understand these things really: the outer view of the senses does not err — the judgement errs if certain forces in the human souls beguile it. The material phenomena do not say to us that they are only matter. The human souls judge about that which is a manifestation of the spiritual that it is only matter. In these human souls certain forces work, which daze them in such a way that they cannot realise that the material is only the expression of the spirit. That which Goethe expressed corresponds to a real being in the human soul: the ahrimanic or Mephistophelian forces work in the soul; and if one discusses these things, one gets quite appropriately to the quotation that the materialist attitude is true evidence of those forces to the spiritual researcher that veil the spiritual to him. These Mephistophelian forces make the human beings shy away from the spiritual.

Source: Rudolf Steiner – GA 69a – Errors of Spiritual Research – Part 2 – Stuttgart, 19 February 1913