In addition to Nick's writeup, Heinlein focused a great deal on competence and understanding. His belief was that in order to lead, one had to experience.

Take an hypothetical city. Populate it with hypothetical people. Give these people jobs to accomplish, thereby creating a functioning (hypothetical) economy.
However, after a certain amount of time has elapsed, the social structure of the city collapses upon itself, due to lack of self-regulation.

Restart city. Create city council to moderate economic exchange. City council is composed of government sleaze who did nothing in previous city (except stagnate).
Of course, the city now falls into corruption.

Heinlein's governing body is composed of people who have worked their way through the ranks, gaining a modicum of experience in all of the subclasses they command. Such a organization would maintain cohesion by sheer force of loyalty, since the senior holders of office would have passed through all of the positions they command.