T. Austin-Sparks emphasizes the essential service of the church as the body of Christ, which is called to fulfill God's divine purpose of filling all things with His presence. He illustrates this through the story of Esther, highlighting that the church is not merely for its own benefit but is a ministering instrument for the good of others. The sermon stresses that every individual in the church has a responsibility to contribute to the body, using the gifts given by Christ to build up the church and reach the fullness of Christ. Sparks warns against a self-centered approach and encourages believers to actively engage in their calling as ministers of Christ. Ultimately, the church's mission is to be a channel of God's grace and life to the world.