Concerning the Spiritual in Art, 1910
And so at different points along the road are the different arts, saying what they are best able to say, and in the language which is peculiarly their own. Despite, or perhaps thanks to, the differences between them, there has never been a time when the arts approached each other more nearly than they do today, in this later phase of spiritual development.
In each manifestation is the seed of a striving towards the abstract, the non-material.
Consciously or unconsciously they are obeying Socrates' command - Know thyself. Consciously or unconsciously artists are studying and proving their material, setting in the balance the spiritual value of those elements, with which it is their several privilege to work.