To live in the kingdom of God is to have God as my king, my ruler, my Lord. To live in the kingdom of God is to have all the scattered parts and pieces of me come under the Lordship of Christ. Our thoughts & feelings, actions, and desires all need to come under the rule and reign of Jesus. Thomas Aquinas taught that there are three aspects to a person: your beliefs, your actions and your affections. In other words, what you think, what you do, and what you desire.
American Christianity has a long history of focusing on right beliefs and right actions, with very little concern for the affections or the desires. The problem that can develop when you disregard affections or desires is you can end up with a nation of cultural christians. These folks may say “I believe Jesus died and rose again, I’ve invited him into my heart, and I go to church every week.” These are good, moral people with the “right” beliefs and the “right” behaviors. But if you could peel back the layers you would find stadiums full of people who wear the “christian” label but whose real desires are all wrapped up in the American dream — not the kingdom of heaven. If you could peel back the layers you’d see where our affections truly lie — that they are all too often wrapped up in desire for power and money and fame and security and comfort. Maybe we have the right beliefs and maybe we are seeking to do the right actions, but our real affections, our real desires are far from aligned with the values of the kingdom of heaven.
Truth comes to you and me in the person of Jesus and says these affections matter. Your desires matter. Jesus comes to us and says, I want to heal and cleanse you from the inside out so that you live with both feet in the strong and unshakable kingdom of God.