Mechanical Function
Every Role provides two things: Narrative Permission, and Improved Effectiveness.
Some things need a Role to even attempt. A Loremaster might recall obscure historical details; others are limited to common knowledge. Only a Spellweaver can learn and cast spells.
When your Role applies to a situation, add its rank to your EL. This makes you significantly better at the things your character does. Anyone can swing a chair, but a Warrior adds all their Role ranks, and has a few other tricks as well.
Within a Role you can learn relevant skills to improve your use of Role-specific behaviors. Warriors can learn to use swords effectively; everyone else is just faking it.