When values are articulated but ignored, an important part of the shared vision effort is shut away. It becomes easier to speak honestly, or to reveal information, when people know that these are aspects of agreed-upon values. Whether you call it a mission or purpose, it represents the fundamental reason for the organization's existence. You will never get to the ultimate purpose of your organization, but you will achieve many visions along the way. Every shared vision effort needs not just a broad vision, but specific, realizable goals.
Goals represent what people commit themselves to do, often within a few months.