Every organization has a mission, a purpose, a reason for being.
Often the mission is why the organization was first created to meet a need identified years ago. Sometimes, the same problems that the organization initially tried to address continue to haunt generation after generation. In that case, the organization's purpose doesn't change although how it does business has probably evolved. Other times, even 10 or 20 years can change the landscape so markedly that the original mission must be updated, altered, or changed dramatically in order to address those new realities. That your organization's mission is current, alive, and well, however, doesn't necessarily mean that the organization has translated that purpose into a clear, concise mission statement.