Okay, to be completely accurate, not everyone in Medina's house deserves the title of Spiritual Advisor. In fact, it's really only Medina who does since her sisters are pretty much opposites, but their opposition is instructive.
Elissa is the eldest and her name means "too little" or "inferior" in Greek. Perissa is the youngest and her name means "too much" or "excessive." So we can understand Medina and her sisters to represent a spectrum: Elissa embodies the extreme of not enjoying anything every (total downer), Medina represents a sensible middle ground and Perissa represents the extreme of enjoying everything way too much. In the language of Goldilocks: too small, too big, and juuuust right.
Considering that we meet Medina and company in Book 2, the Book of Temperance, it all makes sense. Temperance, we might remember, is closely linked to taking a middle ground and avoiding extremes. Medina's overall rationality, kindness, and ability to arbitrate and pacify everyone speaks to the awesomeness of being moderate. You know what else speaks to the awesomeness of being moderate? Porridge that is neither hot nor too cold.