Magical Compendiums

This term refers to a foundation that gives birth to magic.
In particular, it indicates a system trough which magical power can be gained automatically by sharing.
For witches, committing one's magical compendium to paper and leaving it behind for future generations is often considered to be an important life's work.

However, the more fearsome the power of a magical compendium, the harder it is to comprehend and share with others.

An easily-learned magical power may be easy to share, but such magical compendiums are doomed to end up as little more than good luck charms that are eventually forgotten.

The essence of sorcery is maintaining a balance between these two outcomes when leaving a magical compendium behind for later generations.

Magical compendiums are narratives

Magical Compendiums, or systems of magic, are stories or narratives that validate a set of beliefs. They gain more power the more people buy into them but they can also belong to just one person.

The example given by the author for a grimoire, aka a written magic compendium is very clearly the bible, so massive religions and ideologies fit the definition, but so does Maria's coping mechanism to deal with family issues, to name one.