From Introduction:
This set of playbooks exists as an alternative to some of the classes presented in the Dungeon World core rulebook. The playbooks in this packet are replacement classes for the Cleric, Paladin, and Wizard, replacing them with the Priest, Templar, and Mage, respectively. These three classes were specifically chosen to be replaced because of a common flaw they all share: they all carry over baggage from Dungeons and Dragons that limits or somehow weakens their ability to represent a fantasy man of the cloth, holy warrior, or kooky wizard. The main hangups with the original classes are the Vancian casting of The Cleric and The Wizard, which does not represent modern fantasy in the slightest, and the various alignment based mechanics of The Paladin.
The goal of these new classes is to better represent their archetypes than the core Dungeon World classes do. The Mage should be a more iconic and interesting spellcaster than The Wizard, bound by a focus of magic rather than spells per day. The Priest is less of a warrior than The Cleric and more of an evangelist and miracle worker, bound by the tenets of their god more than anything else. The Templar is as much as inquisitioner and a commissar as she is a holy warrior, spurring her allies on to victory even as she charges onward.