The institution’s mission defines its purpose within the context of higher education, the students it serves, and what it intends to accomplish. The institution’s stated goals are clearly linked to its mission and specify how the institution fulfills its mission.
Page 2 of the Design Template has more information on how that is addressed in the Self-Study Design.
Page 11 of the Standards for Accreditation and Requirements of Affiliation has a detailed description of Standard 1.