Sri Aurobindo
Letters of Sri Aurobindo
09. Transformation of the Physical (2)
You have only to admit that the mind and vital can influence the 
body – then no difficulty is left. In this action of mind and vital on the body faith and hope have an immense importance. I do not at all mean that they are omnipotent or infallibly effective – that is not so. But they assist the action of any force that can be applied, even of an apparently purely material force, but the action may be purely material when it is a question of material objects. But in things that have life or mind or mind and life one cannot isolate the material operation like that. There is always a play of other forces mixed with it in the reception at least and for the most part in the inception and direction also.