John Gill discusses the doctrine of the eternal Sonship of Christ, asserting that Jesus is the Son of God by eternal generation, existing as such before His incarnation. He highlights the historical opposition to this doctrine from various heretics throughout Christian history, including Simon Magus, Cerinthus, and Arius, while also emphasizing the defense of this truth by early church fathers and saints. Gill references scriptural evidence from both the Old and New Testaments to support the belief that Christ's Sonship is eternal and not contingent upon His birth from Mary. He concludes that the understanding of Christ's divine nature and eternal Sonship is crucial for orthodox Christianity.