John Nelson Darby addresses the critical issue of doctrinal purity in his sermon 'Remarks on Failure,' emphasizing the severe consequences of corrupting the gospel. He highlights the Apostle Paul's strong rebuke of those who distort the truth, warning that any deviation from the grace of Christ leads to spiritual ruin. Darby contrasts the laxity of contemporary attitudes towards doctrine with the seriousness of maintaining the integrity of the gospel, asserting that true faith must prioritize God's truth over human reasoning. He calls for a return to the foundational truths of grace and warns against the dangers of legalism and worldly influences within the church. Ultimately, he urges believers to uphold the gospel's purity and to recognize the vital connection between doctrine and moral conduct.

C.H. Spurgeon addresses the challenges of maintaining doctrinal purity within the London Baptist Association, emphasizing the necessity of separating from those who compromise essential truths of the faith. He critiques the attempts at unity that disregard fundamental beliefs, arguing that true fellowship cannot exist without a shared commitment to the core tenets of Christianity. Spurgeon warns against the dangers of compromising one's faith for the sake of unity, urging believers to stand firm in their convictions even if it means standing alone. He highlights the importance of recognizing when unity becomes impossible and the need to prioritize truth over mere association.

Mike Attwood discusses the early church in Smyrna and the significant persecutions faced during 100-300 AD, focusing on the martyrdom of Polycarp, who steadfastly refused to deny Christ even in the face of death. He highlights the dual challenges of external persecution and internal doctrinal errors, mentioning groups like the Ebionites and Marcion, who distorted Christian teachings. The sermon also covers the rise of Gnosticism and the need for a defined canon of scripture amidst these challenges, culminating in the Council of Nicaea and the influence of figures like Constantine and Augustine on the church's trajectory. Attwood emphasizes the importance of doctrinal purity and the historical context of the church's struggles against both persecution and heresy.