What do I mean by the heart? Is it the nervous center in the midst of the breast, the small piece of flesh that doctors call the heart? No, the definition of the heart is that it is the depth of the mind, the mind being the surface of the heart. That in us which feels is the heart, that which thinks is the mind. It is the same thing which thinks and feels, but the direction is different: feeling comes from the depth, thought from the surface. When thought is not linked with feeling it is just like a plant rising up from the earth, the root of which has not gone deep. A thought without feeling is a powerless thought; it is just like a plant without a deep root. A tree the root of which has gone deep into the earth is stronger, more reliable, and so the thought deeply rooted in the heart has greater power. The heart therefore is the factor through which spirits and spirituality are to be attained.