Wassily Kandinsky
Have you heard of the book Concerning The Spiritual In Art By Wassily Kandinsky? It describes Mr. Kandinsky's theory of painting and is a very interesting read. I would like to quote from it: "The spiritual life, to which art belongs and of which she is one of the mightiest elements, is a complicated but definite and easily definable movement forwards and upwards...".
Kandinsky goes on to say that the life of the spirit is represented by a triangle which is growing ever upwards and the true artist is the prophet who stands at the apex of the triangle and draws humanity ever upwards with the vision of his art; truly spiritual art is visionary and prophetic.
Possibly a bit too much power placed on the shoulders of the artist but never the less worth considering in the search for what is true spiritual art.