T. Austin-Sparks emphasizes the significance of proclaiming the Gospel of the Kingdom, which is fundamentally about the royal reign of Jesus Christ. He explains that this proclamation is not merely an announcement but a call to establish evidence of Christ's lordship in the world. The sermon highlights the cosmic conflict between the Kingdom of God and the usurper, Satan, and the necessity for Christians to embody the truth of the Gospel in their lives. Sparks challenges both believers and non-believers to recognize their allegiance to either Christ or the Devil, urging a response to the call of the Kingdom. Ultimately, he stresses the urgency of this mission as the fulfillment of God's plan awaits the testimony of His Church.