Chapter 1 explains the theoretical framework deployed throughout the book, largely drawn from the companion volume, Unearthly Powers. Above all, this means explaining the two forms of religiosity – immanentism and transcendentalism – and how they related to each other. While immanentism is a default or universal strand of human life, transcendentalism defines what is distinctive about the religions of salvation that emerged from the Axial Age of the first millennium BCE. These world religions also contained an immanentist element, however, even as they produced reform movements that insisted on the transcendentalist dimension. These modes also gave rise to two different means by which rulers could be sacralised: divinised kingship (immanentism) and righteous kingship (transcendentalism). The chapter then fleshes out a tripartite model for ruler conversion: (1) religious diplomacy often first induced rulers to favour foreign missionaries; (2) immanent power, or supernatural assistance in this life, tended to be crucial in convincing them to make a change of allegiance, and (3) the Christianisation of their realms was linked to its capacity to enhance their authority. Lastly, the themes of cultural glamour and intellectual appeal are introduced.