In The Next Christendom, one could argue that Philip Jenkins is attempting to provide the reader with a glimpse into the future development of Christianity.
Drawing on extensive historical data, Jenkins sees the future of Christianity in its past, a global religion embracing a wide variety of different cultures and traditions.
In particular, he sees the exponential growth of Christianity in the Southern Hemisphere over the past century as a prelude to the faith's future redefinition. For Jenkins, global Christianity will be defined in the future by the conservative variant currently practiced in the Southern Hemisphere.
Right throughout The Next Christendom, Jenkins challenges the unthinking assumption of those in the West who see Christianity as essentially a religion of the Northern Hemisphere. As Jenkins points out, it was a full thousand years after the fall of the Roman Empire that Christianity became a predominantly European creed.
At no time in history has the West had a monopoly on the Christian faith. That being so, the massive spread of Christianity in the Southern Hemisphere that has taken place over the last hundred years or so should not be seen as an anomaly but as an indication of the truly global nature of the Christian faith.
For Jenkins, then, the past is prologue. His overriding purpose in writing The Next Christendom is to help us realize this crucial point.