A human being is part of a whole, called by us the "Universe", a part limited in time and space. We experience ourselves, our thoughts and feelings, as something separated from the rest -- a kind of optical delusion of our consciousness. This delusion is a kind of prison for us, restricting us to our personal desires and to affection for a few persons nearest us. Our task must be to free ourselves from this prison by widening our circles of compassion to embrace all living creatures and the whole of nature in its beauty.
You know of the disease called sleeping sickness. There also exists a sleeping sickness of the soul. Itsmost dangerous aspect is that one is unaware of its coming. That is why you have to be careful. As soon as you notice the slightest sign of indifference, the moment you become aware of the loss of a certain seriousness, of longing, of enthusiasm and zest, take it as a warning: your soul suffers if you live superficially.