The mission statement should guide the actions of the organization, spell out its overall goal, provide a path, and guide decision-making. It provides "the framework or context within which the company's strategies are formulated." It's like a goal for what the company wants to do for the world. 
Effective mission statements start by cogently articulating the organization's purpose of existence.
Mission statements often include the following information:
Aim(s) of the organization
The organization's primary stakeholders: clients/customers, shareholders, congregation, etc.
How the organization provides value to these stakeholders, for example by offering specific types of products and/or services
A declaration of an organization's sole core purpose. A mission statement answers the question, "Why do we exist?"
According to Bart, the commercial mission statement consists of 3 essential components:
Key market – who is your target client/customer? (generalize if needed)
Contribution – what product or service do you provide to that client?
Distinction – what makes your product or service unique, so that the client would choose you?
Examples of mission statements that clearly include the 3 essential components:
McDonald's - "To provide the fast food customer food prepared in the same high-quality manner world-wide that has consistent taste, serving time, and price in a low-key décor and friendly atmosphere."
Key Market: The fast food customer world-wide
Contribution: consistent taste and reasonably-priced food prepared in a high-quality manner
Distinction: delivered consistently (world-wide) in a low-key décor and friendly atmosphere.
Courtyard by Marriott - "To provide economy and quality minded travelers with a premier, moderate priced lodging facility which is consistently perceived as clean, comfortable, well-maintained, and attractive, staffed by friendly, attentive and efficient people"
Key Market: economy and quality minded travelers
Contribution: moderate priced lodging
Distinction: consistently perceived as clean, comfortable, well-maintained, and attractive, staffed by friendly, attentive and efficient people
The mission statement can be used to resolve trade-offs between different business stakeholders. Stakeholders include: managers & executives, non-management employees, shareholders, board of directors, customers, suppliers, distributors, creditors/bankers, governments (local, state, federal, etc.), labour unions, competitors, NGOs, and the community or general public. By definition, stakeholders affect or are affected by the organization's decisions and activities.