William Cathcart preaches about Novatian, the founder of the Novatians, who was a philosopher before his conversion and became a strong advocate for maintaining purity in the churches. Novatian resisted the forgiveness of apostates by the church, leading to his condemnation by Cornelius and the Roman bishops. The Novatians, also known as Kathari or Puritans, emphasized purity of church membership and excluded those who had committed deadly sins or sacrificed to idols. Despite persecution, the Novatians spread widely and influenced many Christians with their strong stance on discipline and consecration to God.

William Cathcart preaches about the historical context of the Donatists in North Africa during the persecution of Diocletian, highlighting the conflicts surrounding martyrdom, the actions of Bishop Mensurius of Carthage, the rise of the Donatist denomination under Bishop Donatus, and their strong stance on church purity and separation from the state. The sermon delves into the controversies between the Donatists and the Catholic Church, particularly regarding infant baptism, as seen through the lens of Augustine's writings and the Council of Carthage.

William Cathcart delves into the history of the Albigenses, also known as Cathari, Paulicians, and other names, tracing their origins back to Armenia and their spread across Europe, facing persecution and maintaining a strong adherence to the New Testament. The Albigenses were known for their modest and blameless lifestyles, rejecting wealth and living by labor, as well as their emphasis on teaching and circulating the Scriptures in the common language. Despite being labeled as heretics by the Church of Rome, they held firm to their beliefs, including their rejection of infant baptism and their unwavering commitment to the Word of God.

In this sermon, the preacher delves into the meaning of 'witnesses' (martus/martys) in the Bible, highlighting the dual role of a witness as one who has seen or experienced something and one who testifies to what they saw. The sermon emphasizes the importance of being a witness in legal settings and in recounting firsthand knowledge. It also explores how witnesses in the Bible attest to facts, give evidence, and confirm truth through verbal testimony. The preacher connects the concept of witnesses to the Old Testament 'formula' of 'two or three witnesses' and discusses how witnesses in Hebrews 11 exemplify faith in God. The sermon concludes by discussing the significance of being a witness for Jesus, even to the point of martyrdom, and how the power of the Holy Spirit enables believers to be effective witnesses to the truth of God and His coming judgment.

William Cathcart preaches about Peter de Bruys, a Catholic priest turned preacher of the gospel in the 12th century, who vehemently opposed Roman Catholic practices. Peter taught that only believers should be baptized, rejected the presence of Christ's body and blood in the Eucharist, and denounced prayers for the dead. He led a movement that destroyed crosses and churches, emphasizing a simplistic worship devoid of idolatry. Despite facing opposition from ecclesiastics like Peter the Venerable, Peter de Bruys successfully converted many to a more Scriptural faith, challenging the authority of popes, bishops, and priests.

William Cathcart preaches about the history and principles of the Anabaptists during the Reformation, highlighting their rejection of infant baptism and their emphasis on believers' baptism as the only Christian baptism. The Anabaptists sought to establish churches based on regenerate church membership and separation from the ungodly, believing in the necessity of personal faith before baptism. The sermon delves into the divisions among Anabaptists, including the fanatical, Baptist Anabaptists, and mystical Anabaptists, shedding light on their struggles, beliefs, and influence on the Reformation.