Just as in the body, eye and ear develop as organs of perception, as senses for bodily processes, so does a man develop in himself soul and spiritual organs of perception through which the soul and spiritual worlds are opened to him. For those who do not have such higher senses, these worlds are dark and silent, just as the bodily world is dark and silent for a being without eyes and ears.
Theosophy: An Introduction (ed. Simon and Schuster, 2012) - ISBN: 9781625581228