Purpose:

For a nonprofit organization, there must be identifiable social or political needs that the organization seeks to fill. 
 

Approaches:

Development of the mission statement should grow out of lengthy discussions about the organization's identity, its abiding purpose, its desired response to key stakeholders, its philosophy and core values, and its ethical standards. 
 

John M. Bryson, Strategic Planning for Public and Nonprofit Organizations:  A Guide to Strengthening and Sustaining Organizational Achievement, rev. ed. (San Francisco:  Jossey-Bass, 1995), 26-28.