J.C. Ryle's sermon 'The Great Separation' emphasizes the ultimate division of humanity into two classes: the 'wheat' representing true believers in Christ and the 'chaff' symbolizing those without faith. He warns that a day of reckoning is coming when Christ will separate the righteous from the unrighteous, and only those who have genuinely accepted Him will be gathered into His barn, while the rest will face eternal punishment. Ryle urges listeners to examine their own hearts and recognize the reality of their spiritual state, as neutrality is impossible. He reassures believers of Christ's unwavering care and the promise of eternal life, while also solemnly warning the unrepentant of the dire consequences of their choices. The sermon serves as a call to repentance and a reminder of the urgency of faith in Christ.