When a child is born and brought up, its first tendency is to enjoy and experience all that is outside itself, and the man usually gets no chance to experience what is within himself. But at the same time the body is equipped with the instrument, with the means, by which to experience both the life outside and the life within. If a person does not use his hand or his leg for many years, the outcome will be that it loses its vitality, life, energy, and will no longer be of any use. We know the use of our hands and feet which are outer parts of the physical mechanism, but there are inner and finer parts of the physical mechanism which mystics have called centers, each center having its particular object -- intuition, inspiration, impression, revelation -- which are all realized through the medium of these centers.