The Next Christendom by Phillip Jenkins is an examination of the spread of Christianity, how its power became centered in the Northern Hemisphere of the world, and the current movement to its next stage, where Jenkins sees its power centered in the Southern Hemispheres of Africa and South America. This, he posits, will be due to population growth of these areas, while at the same time the Western population stabilizes. The poor and oppressed in the developing nations of the Southern Hemisphere will be drawn to a new, more vital, localized version of Christianity, Jenkins believes.

Jenkins observes how Christianity in the West has morphed into a 'comfortable' religion, where people are economically well off and liberal views have become incorporated into the Christian idea of acceptance and brotherhood. But in South America and Africa, there has been an ongoing trend towards a more passionate and conservative Christianity, one that harkens back to the earliest days of the Pentecostal, post-crucifixion followers of Jesus. These earliest Christians were a marginalized group who drew heavily on prayer as a source of addressing fundamental problems, and they also found a lifeline of tight-knit support in their community. Similarly, Christians in South American and African countries are finding a more practical, essential Christianity than we often see in the West. Jenkins notes that in this revival, local beliefs such as ancestor worship, for instance, are sometimes conflated with Christian ideas, which he accepts as a valid adaptation of Christianity absorbing new cultures. Much of Christian mythology from its beginning was in fact merged with early Roman and pagan beliefs: the virgin birth, December 25 as Jesus's birthdate, and other beliefs. Jenkins worries that these newly accepted local customs will be looked at as backward and non-Christian, and cause a widening divide between Northern and Southern World Christianity.

He also foresees a possible future global conflict between Muslim and Christian nations, as each group grows in population. Neither side, he observes, will be likely to convert to or accept the validity of the other, especially with the inherent fundamentalist tendencies embedded in each belief. The somewhat hopeful note Jenkins sees in this rather dark scenario is that large shifts in understanding of religions can occur, causing a re-examination of both the differences and similarities existing in established beliefs. Jenkins sees in-depth understanding as the starting point to any possible reconciliation of opposing beliefs.