From the publisher's website:
Divine magic is one of the most common components of the Pathfinder Roleplaying Game. Humble adept NPCs, evil humanoid shamans, heroic clerics, and stalwart paladins alike use it. Divine spells call to mind major events in popular games and fictions, ranging from the summoning of demons and otherworldly allies to the power to heal, curse, and even raise the dead. Divine spells are the tools used in most campaigns to represent the world’s magic of lore, restoration, and communing with the gods. A great deal of the tone of fantasy in a campaign stems from those who use divine magic and where one finds it.
Fantasy stories are full of warriors who have been trained to face supernatural evils, mad prophets who call upon powers no one understands, and failed priests who still recall a few of their prayers of healing and discovery. Such characters can be built, at least sometimes, with the multiclassing rules and prestige classes, but such efforts often feel awkward and might not make sense when a character’s entire backstory is taken into account. In a core rulebook, the number of character options that can be presented is limited, but many players quickly crave more flexibility.
The Genius Guide to Divine Archetypes provides the material necessary to give spellcasting classes new forms of arcane magic or to add arcane power to classes that normally lack it. It does this through the use of archetype packages—a way to replace a set of related class abilities normally included in base classes with new powers (in this case, tied to arcane magic). These archetype packages can change how magic works for a character (such as the gnostic archetype), add an element of divine spellcasting to characters who normally lack it (such as with the wise and witness archetypes), or grant wholly new divine powers to characters based on the flavor of their faith (such as the chantry and exorcist archetypes).