John Nelson Darby discusses the challenges faced by the Corinthian church, emphasizing their carnal state and inability to receive deeper spiritual truths. He contrasts the building of God's church with human efforts, highlighting the importance of being mindful of how one builds upon the foundation of Christ. Darby illustrates that while all believers are part of God's temple, the quality of their works will be tested, and those who introduce false teachings risk defiling the temple. He stresses the need for personal attachment to Christ to truly understand and communicate His message. Ultimately, the sermon calls for discernment in spiritual matters and a commitment to building according to God's design.