N.T. Wright
People are expecting that God is going to send in the troops, but Jesus is saying God becomes king in the same way he wanted creation itself to work in the beginning—by seeds being sown. This is what God's kingdom is like. It's like a woman who loses a coin and finds it again. It's like a shepherd looking for sheep. It's not like clearing out the sheep over night and getting a new lot who will never ever get lost.
In the first three centuries, when the Romans were persecuting [the church] beyond belief, people still went on becoming Christians because the church was out there doing stuff. They were caring for people by looking after the poor and the lonely and the elderly. People were just flabbergasted because they had never seen anything like this before. Nobody had ever looked after, or educated, or cared for people other than their own kin or immediate special interest groups. The thought that there was a community that was just going around doing good—especially to the poor—just freaked people out.
What we've forgotten in the West—because it's in the interest of post-Enlightenment Western society to forget it—is that the church has actually radically transformed the world. For example, most of the great hospitals and educational institutions have been started by Christians . . . that's the kind of stuff the church does. These are signposts of the kingdom. This isn't bringing the kingdom in all its fullness. Only God will do that in God's good time. But God has begun to do it through Jesus, and he's continuing to do it through the Spirit.
When God wants to run the world in his way, he doesn't send in the tanks. He sends in the meek, the mourners, the peacemakers, and the people hungry for justice. By the time the bullies wake up and realize what's going on, they have set up schools, built hospices, made peace, and brought warring armies back together again.