The Arcanist's Guild
Selera’s view of mages is questionable at best, violent at worst. Destroyed villages, undead roaming the plains, and areas that will forever be magically altered are the work of a loud minority that do not represent the whole of the magical community. The Arcanist’s Guild exists to give mages a chance to fit in.
Originally created as a prison, per request of the then emerging Cloister, mages were to be locked in a tower in which they could not harm the world. However, as time went on, and as it became clearer that mages were truly helpful, the runners of the “prison” convinced the temple to allow them to register responsible and morally upright mages who could control their power. This license, given by the guild, is the one thing that prevents magical individuals from being hunted down and imprisoned. This makes it necessary for all mages to be part of the Guild, and all mages to be certified by the Guild. In addition, if the Guild (or the temple, or even The Cloister) finds it necessary, blood is provided to make for easy scrying.
Everyone who joins the Arcane University automatically joins the Arcanist’s Guild, and everyone who knows magic will join the Arcane University, even if The Cloister has to pull mages from their families to do it.