From that time Jesus began to preach, saying, “Repent, for the kingdom of heaven is at hand. (Matthew 4:17)
Jesus commands us at the very beginning of His ministry to repent. The word repent is actually the Greek word μετάνοια, or metanoia. It essentially means to ‘think differently after,’ or to change the mind. Change the mind from what? Our current ways, which are sinful. Why? Because the kingdom is at hand, and because that kingdom is ruled by God, and because God does not tolerate sin.
This is what the Apostle Paul was talking about when he said, “Do not be conformed to this world, but be transformed by the renewal of your mind” (Romans 12:2). Our thoughts determine our actions, our actions determine our behavior, and our behavior defines us. Christ commands us to turn away from our sinful thoughts, the thoughts that the rest of of the world have, in order that our actions might change so that, ultimately, we may be defined as Christians, which is the only way into the kingdom.
If you love me, you will keep my commandments. (John 14:15)