Now I am speaking to you, but you would not hear me if my voice were not able to produce vibrations in the air. Thus every word which I utter exists in the air in the form of fine movements. These fine movements of course vanish, but everything which occurs here on earth becomes impressed in that fine substantiality which we experience when reaching the spiritual world. This impression is everlasting. Every word, every thought, everything which has ever taken place in humanity, can be read in the Akasha Chronicle.
Source: Rudolf Steiner – GA 100 – Theosophy and Rosicrucianism: Lecture IV: Man’s Further Destinies in the Spiritual Worlds – Kassel, 19th June, 1907