What do you wish to accomplish through your business and for what purpose? This is the general idea of a mission statement. It is a fairly brief, written statement with an altruistic aim designed to reflect a focus outside the obvious creation of profit and capital.
The mission statement drives the general direction of the business and provides the overarching philosophy that will filter down from executive management throughout the staff and influence motives, choices and actions.
For example, “Our Mission is to provide superior (product, service, leadership, etc. …this is what you want to accomplish) that will enable our (clients, customers, patrons) to (improve their health, achieve their goals, become self-sufficient. … this is the purpose) with the goal of building a lifelong business relationship” (influencing motives, choices and actions of staff).
To answer your second question, yes. Every business should have a mission statement. It provides a focal point, a focus for management as well as staff.