Evangelicalism is reaching an inflection point. The exodus of millennials from Evangelical churches and the growth of those self-identifying as "Nones," as in "None of the Above," for their church affiliation, is concerning for the movement's future. Evangelical leaders offer mixed responses to this challenge--from circling the wagons to an enthusiastic "Everything must change!" posture. Theosis takes a different approach. Seeking to understand Evangelicalism and its origins, this book suggests that Evangelicalism is best understood as the sibling of western, Enlightenment Modernity, which served it well . . . until the modern cultural ethos began to shift dramatically toward post-modernity. In this shift, young Evangelicals--principally postmoderns themselves--are abandoning "their father's Evangelicalism" and its perceived linearity, hyper-rationalism, either/or exclusivity, and faith expression, too often perceived as stripped of mystery and wonder. Theosis proposes that to move forward, Evangelicalism must go back to the future, to re-engage with the patristic understanding of salvation as theosis; deification, or union with God. This radical return--and broadening of the doctrine of salvation--has begun to gain traction in Western Christendom, slowly being considered as it has always in the Christian East, as mere Christianity.