Theodore Epp emphasizes that spiritual unity within the Body of Christ is not automatic and must be rooted in the truth of Scripture. He warns against the dangers of ecumenism that prioritizes unity over doctrinal truth, which can lead to a dilution of the Gospel message. Epp stresses that while organizational unity among believers is acceptable, compromising biblical truths to achieve unity with unbelievers is not. He encourages believers to diligently strive for harmony, as true unity is maintained through fellowship with Christ. The sermon concludes with a reminder of the beauty of unity among brethren as expressed in Psalm 133:1.