The following is copied in from Wikipedia.

A commissariat is a department or organization commanded by a commissary or by a corps of commissaries.

In many countries, commissary is a police rank. In those countries, a commissariat is a police station commanded by a commissary.

In some armies, commissaries are logistic officers. In those countries, a commissariat is a department charged with the provision of supplies, both food and forage, for the troops. The supply of military stores such as ammunition is not included in the duties of a commissariat. In almost every army the duties of transport and supply are performed by the same corps of departmental troops.

The Cloud Spires royal houses each provide soldiers who are specially trained to become members of the commissary in Royals Peak.

Each house may provide up to three members, although most provide a single champion, or none at all since Faramore Barl stepped into the role of militia captain, and subsequently the city guard.

With Faramore, a local celebrity, leading the training and maintenance of a primary defense and security force that the houses could count on, the council effectively wrote a blank cheque and the commissariat has dwindled to a trio of 'champions' (including Ivor Keterog, and several retired officers.

Commissary is typically a role for life, or until the body is incapable of providing the people their justice and protection.

Enrolment in another organization does not nullify membership, but refusal to answer the call, without officially denouncing ones position in advance, is seen as a treasonous act.