Purity of mind is the principal thing upon which the health of both body and mind depend. The process of purifying the mind is not much different from the process of cleaning or washing any object. Water poured upon any object washes it, and if there is a spot which cannot be washed away by the water, some substance which can take away that spot is applied, to wash it thoroughly. The water which washes the heart is the continual running of the love-stream. When that stream is stopped, when its way is blocked by some object which closes the heart, and when the love-stream is no longer running, then the mind cannot keep pure.