John Gill emphasizes the apostolic testimony regarding the love and grace of God as revealed through Jesus Christ. He explains that while no one has seen God's essence, the apostles witnessed Christ's love, miracles, and resurrection, affirming that He was sent by the Father to be the Savior of the world. Gill clarifies that this salvation is not universal for every individual but is specifically for the elect, encompassing believers from all nations and backgrounds. He highlights Christ's role as the complete Savior, delivering believers from sin and its consequences. The sermon underscores the importance of recognizing and testifying to the truth of Christ's mission.