John Gill emphasizes that while no one has seen God in His fullness, we are called to express our love for God through our love for one another. He explains that God's presence dwells in those who love each other, reflecting the Spirit's work in their lives. Gill further clarifies that God's love is perfect and unchanging, while our love for Him and others is a growing and sincere expression of faith. The sermon highlights that true love is demonstrated through actions, not just words, and that our love for fellow believers is a reflection of our love for God.