The Parable of the Worldwide Saturation of Christianity (Parable of the Mustard Seed)

In the parable of the mustard seed, Jesus taught us that the kingdom of heaven would grow on the earth and grow and grow and grow until it becomes the largest of all garden plants (i.e. kingdoms). In other words, Christianity, will one day saturate the entire earth and be the most powerful and dominant influence in the whole world. Doesn't seem possible, I know. We in America are languishing under the decline of Christianity in our nation. But the kingdom is growing in other parts of the world, and one day it will fill the whole earth. That is the clear teaching of the parable. Does your eschatology have a place for this truth?