The only thing we may bring into the spiritual world is thoughts.

Rudolf Steiner, November 13, 1909:

"What is it that can prevent one from losing vision altogether on entering actually into the spiritual world? The seed that can spring up out of thinking! Thoughts afford the substance whereby what is in the spiritual world may be comprehended. We acquire the power really to live in the spiritual world by comprehending, in our world of the senses, what is no longer permeated by sense-elements and yet is on the physical plane. Thoughts alone fulfill this condition. The only thing we may bring into the spiritual world is thoughts."