By being the "calm center" around which the kingdom turns, the king allows everything to function smoothly and avoids having to tamper with the individual parts of the whole.
This idea may be traced back to early shamanistic beliefs, such as that of the king (wang, sa) being the axle between the sky, human beings and the Earth. (The character itself shows the three levels of the universe, united by a single line.) Another complementary view is that this idea may have been used by ministers and counsellors to deter aristocratic whims that would otherwise be to the detriment of the population.
Although Confucius claimed that he never invented anything but was only transmitting ancient knowledge, he did produce a number of new ideas. Many western admirers such as Voltaire and H.G. Creel point to the (then) revolutionary idea of replacing the nobility of blood with one of virtue. Juniz which had meant "noble man" before Confucius' work, slowly assumed a new connotation in the course of his writings, rather as "gentleman" did in English.
A virtuous plebeian who cultivates his qualities can be a "gentleman", while a shameless son of the king is only a "small man". That he allowed students of different classes to be his disciples is a clear demonstration that he fought against the feudal structures in Chinese society.