Thus the law enforcing agencies, the soldiers and militia fall in this category of courage. The third part is self-discipline. Socrates explained that it is not easy to allow oneself to be ruled. But when every section of a community accepts its rulers and understands that some people rule while others are the ruled, they are exhibiting self-discipline. This is needed for a community to function smoothly. When all these elements are found, we realize that the ability to a community to allow every person to do his job without creating conflict is morality. This is the outer morality that helps keep a community intact.

In almost similar fashion, the person must function smoothly and remain intact too. Any conflict within a person's mind would create discord and this would lead to immorality. Socrates introduces his tripartite philosophy in this case and explains that the mind is divided into three elements just as the community was. "we've reached the reasonable conclusion that the constituent categories of a community and of any individual's mind are identical in nature and number." (p. 152) These parts are three desires or instincts. The desire to fulfill basic needs, the desire for self-preservation and the desire for knowledge, understanding and truth. However each desire is backed by reason though this reason may not be of the same kind as that residing in the rational side of mind. It is important to acknowledge reason and allow each desire to function properly without any side ruling or enslaving the other. This harmony results in morality. Any discord in this area would result in immorality. Socrates concluded by saying: "Where each of the constituent parts of an individual does its own job, the individual will be oral and will do his own job." (153)

Inner and...

They cannot be fully understood without grasping the gist of tripartite. Socrates is correcting in pointing out that harmony is the essential requirement of morality. It cannot exist where discord exists. However what Socrates is talking about is an ideal state or community. In modern times, we hardly see any evidence of that ideal state existing anywhere in the world. This has definitely led to serious conflict and disharmony and immorality and anarchy are common. From our own observation of the world, we can say that Socrates was correct in his description of morality. Instead of measuring morality with the yardstick of goodness or sin, he is simply referring to the principles of harmony and discord. In my personal opinion, I have noticed that this harmony is very important for morality to exist. A person who is confused about the laws of the state, laws of religion and any other rules given by authorities would try to transgress a few times. He doesn't really want to create discord but is not sure about those laws. He may not always accept that something that is to be feared must be feared. He might wonder why this law was created or why that rule is to be followed. If he comes to understand that these laws and rules are based on a higher reason and serve an important purpose, then he would be at peace and this would stop him from breaking the laws now and then. Thus for morality to exist, it is important that every single part of the community and mind must be allowed to function properly within its own limits. This would create harmony and peace and these two are the essential components of inner and outer morality.
Reference:

Plato. Republic. Robin Waterfield (Translation) Oxford University Press. Oxford.1994