The problem with mission
A tried and true organizing step is to create a mission statement. A mission statement, which is also sometimes called a purpose statement, expresses what the organization is about, it's theme if you will, its hallmark.
The mission of Franklin Covey is, "We enable greatness in people and organizations everywhere." For Wal-Mart it is: "We save people money so they can live better." For Patagonia, it is: "Build the best product, cause no unnecessary harm, use business to inspire and implement solutions to the environmental crisis."
Statements such as these - and the many that are longer and more involved - can be descriptive and inspiring. They look good on the wall, the business card and the page in the annual report. They are "feel good" words.
However, in and of themselves they are insufficient. They are by their very nature about the current organization. They lack specificity. They tend not to drive change.
Certainly, saying "Here's what we do" is of value as a descriptor for external and internal use. It reminds all of why the organization exists and what business it is in. That does have focusing effects.
The rub is that strategic planning starts with the fundamental premise that the current state of the organization is not ideal and that what the organization is doing now is sub optimal. The organization may (or may not) be in a desirable business - what the mission statement describes - but how it is going about that business and its expectations about that business and where it is trying to go with that business likely are not ideal.
A mission statement describes what is. A vision statement describes what can be.
A compelling vision statement is most important in laying out that "shining city on a hill" where the organization wants to go. It starts with the premise that the future can be better and the organization needs to act and change to get there. Putting a compelling vision of the future out there enables every possible action of the organization to be evaluated: How will this get us there? It makes the directional changes and investments necessary for positive change more apparent.
Yes, indeed, craft your mission statement and let all know what business you are in, your hallmark. But please don't stop there. Think about that great place the organization can be 3-5-7 years in the future, write a compelling vision statement, and use that vision statement to drive your organization forward to a better future.