A more thorough explanation:

DIOCESAN MISSION

A diocesan mission is a mission that operates within a single diocese.

• A church that provides food and shelter to homeless people within its diocese.
• A charity that raises funds to support education programs in a specific diocese.

These examples illustrate how a diocesan mission focuses its efforts on serving the needs of a particular diocese. The church and charity mentioned above are both working to improve the lives of people within their local community, rather than spreading their resources across multiple regions or countries.