T. Austin-Sparks emphasizes the theme of 'Consummated Union' in his sermon, illustrating how God's original intention for humanity was to be transfigured and glorified through Christ. He explains that through the union with Christ, believers are destined for glory, which is not just a future hope but a present reality experienced through the Holy Spirit. Sparks highlights the transformation of our physical bodies and the corporate glorification of the Church, culminating in the ultimate vindication of Christ in His saints. He encourages believers to recognize that their union with Christ is the foundation for experiencing glory in their lives, even amidst trials and suffering. The sermon concludes with a call to live in the present reality of this glory, empowered by the Holy Spirit.