No doubt many of you, as children, would have been given the following exercise. For a month's wages, would you prefer to be paid (a) $1,000 a day, or (b) one cent the first day, two cents the second, and so on, doubling the pay every day? If you chose the second option, you would receive only a paltry $5.12 on day 10, but for day 30 your wages would be more than half a million dollars. Such is the magic of exponential growth.
Now, consider the one cent on the first day as the mustard seed of Matt. 13: 31-32. If a religion grows by just 50% per generation, relative to the population, then, from a baseline of a few hundred or few thousand followers, it will remain insignificant for a long time. But once it reaches one percent of the population, it is on track to reach five percent in 100 years, and 25% in 200. And in 300 years ...? And there is also evidence that, at specific times and places, Christianity have expanded much faster. In The Rise of Christianity, Rodney Stark has demonstrated that the history of the religion in the Roman Empire is consistent with a growth rate of 40% per decade. Thus it was that, by the third century, the Roman authorities discovered that a movement, originally no more than an irritant, was now too large to stop. Closer to our own times, in the 1980s, commentators began to notice that sub-Saharan Africa was rapidly turning Christian.
Why do I mention this? Because it appears that exactly the same thing is being played out right now in the largest country on earth.
