If the book we are reading does not wake us, as with a fist hammering on our skull, why then do we read? So that it shall make us happy? Good God, we should also be happy if we had no books, and such books as make us happy we could, if need be, write ourselves. But what we must have are those books which come upon us like ill fortune, and distress us deeply, like the death of one we love better than ourselves; like suicide. A book must be an ice-axe to break the sea frozen inside us.
Each thing tends to move towards its own nature. I always desire happiness which is my true nature. My nature is never a burden to me. Happiness is never a burden to me, whilst sorrow is.
Material objects give rise to physical happiness, while spiritual development gives rise to mental happiness. Since we experience both physical and mental happiness, we need both material and spiritual development. This is why, for our own good and that of society we need to balance material progress with inner development.