John Gill emphasizes the critical importance of acknowledging Jesus as the Christ, the true Messiah foretold by the prophets. He argues that denying Jesus' messianic identity is the greatest lie, as it contradicts the undeniable truth supported by Jesus' own declarations, the testimonies of the apostles, and divine affirmations. Gill warns that those who reject Jesus in any of his roles—prophet, king, or priest—are not only liars but also antichrists, opposing the very essence of the Christian faith. He highlights that even the devil recognizes Jesus as the Christ, making those who deny Him the worst of deceivers. The sermon serves as a strong reminder of the necessity to uphold the truth of Christ's identity and the implications of denying it.