John Nelson Darby emphasizes that Christians are representatives of Christ, as evidenced by the transformative power of the truth in their lives. He addresses the Corinthians' doubts about his apostolic authority by pointing to their own conversion as proof of his ministry. Darby explains that true Christianity is not merely about outward conduct but about having Christ engraved on the heart through the Holy Spirit. He contrasts the ministration of the letter, which brings condemnation, with the ministration of the Spirit, which offers righteousness and freedom. Ultimately, believers are called to reflect Christ's love and grace in their lives, serving as living epistles to the world.