A city without walls was a disaster waiting to happen. Without a defense, any enemy that approached could inflict severe harm. It mattered not how beautiful the houses were or how magnificent the edifices appeared in the interior. If there were no walls, there would be no peace. Without peace, there could be no long-term prosperity.
Some people make great efforts to better themselves. They obtain an education, apply for good jobs, get married, begin a family, and join a church. Yet they do not effectively control their own spirit. As a result, they lose their temper, or speak cruelly to others, or fail to demonstrate self-control. As a result, all that they have built in their life is assaulted and torn down. Years of labor can be ravaged in moments. People who do not control themselves are taking one step forward and then two backwards.
Ruling over our spirit should not be done haphazardly. It is a decision we make each day. Because we controlled our spirit yesterday does not mean we will effectively rule our spirit today. Carefully build strong walls around your life so you protect all that has been constructed over a lifetime.