A non profit mission statement contains the general philosophy, general goals, and major specific benefits that the organization provides to the community, the nation,or the world. The mission of the organization, once well defined, serves as a template for everything that the organization does. Any major deviations from the mission require a major change to the mission statement.
The major areas of importance in mission statements include: clarity of language in describing and presenting the face of the organization to the public and to benefactors; serving as a template for projects and programs to prevent goal diversion; and serving as a template to prevent goal displacement, which can lead to confusion and the ultimate breakdown of non profit structure.
As a template for everything that the organization does, every specific project or program should be easily related back to the well designed mission statement. When a major project is taking up all of the time, staff and resources of the organization, but the project cannot be related to the mission statement, no matter how twisted the logic, a problem called "goal diversion" has happened.
For various reasons, from board members who throw their weight around in order to get a project added to the pile, to the executive director who never intended for the organization to stay the same, to the grant award that requires a major overhaul in the way that the organization does business, goal diversion and goal displacement is a common trap for many non profits.
Well designed and updated mission statements help to prevent uncontrolled goal diversion, goal displacement, and complete confusion when everyone tries to figure out how an organization got so far off of the tracks. When a board member has an unplanned opportunity to meet with or speak with someone who could end up being a major benefactor, a lucid, articulate and coherent summary of the mission statement, without sounding like one is reciting something that has been memorized, can be the difference between an unexpected grant and a reputation for having an inarticulate and out of touch board of directors.
Thus, the well crafted mission statement is understandable, eschewing impressive sounding wording for clear language which anyone can quickly read and digest. That leaves the final element of the importance of a well designed mission statement: clarity and focus that allows representatives to put the best face forward, when discussing or describing the organization.