Christianity is interested in change from the inside out. It's not the external but the internal. So great changes can occur but still be unseen. Jesus illustrated that truth in one of his kingdom parables.
33 He spoke another parable to them, "The kingdom of heaven is like leaven, which a woman took, and hid in three pecks of meal, until it was all leavened." (Matthew 13:33)
Romans 12 used the Greek word metamorphosis to explain how believers change. A metamorphosis is a complete change from the inside out, everything is affected. When the Christian metamorphosis is complete, the world sees something completely different. People are in love with great schemes, power, and wealth and those are the tools they use to change the world.
So what Jesus is telling us is that if we want to change this world we must do it from the inside out. We change the world by giving the gospel and doing good works. Doing that does not look as impressive as power and wealth, but the results are eternally permanent and richly personal because they change the heart. So start changing the world from the inside out.