Whenever you craft, upgrade or grind Equipment, you'll get EXP for your Meister Level.
High Meister levels will help you craft better Equipment or give you more advantage when you upgrade.
There are total 6 kinds of Meister Levels: Helmet, Garment, Gloves, Boots, Weapon and Accessory.
You'll get Gems of the Abyss, Silver and Equipment Materials for that Meister Level whenever you level it up.