Doctrine of the Mean, Chapter 1, in Wing-Tsit Chan, Chinese Philosophy, Chapter 5.
In the above first chapter, Tzu-ssu (Confucius grand son, author of the Doctrine of the mean according to Chu His) relates the ideas which had been transmitted to him, as the basis of discourse. First, it shows clearly that the origin of the Way is traced to Heaven and is unchangeable, while its concrete substance is complete in ourselves and may not be departed from. Next, it speaks of the essentials of preserving, nourishing, and examining the mind. Finally, it speaks of the meritorious achievements and transforming influence of the sage and the spirit man in their highest degree. Tzu-ssu's hope was that the student should hereby return to search within himself to find these truths, so that he might remove his selfish desires aroused by external temptations, and realize in full measure the goodness which is natural to him. This is what scholar Yang meant when he said that this chapter is the quintessence of the whole work.