Christian theology is reasoned commentary concerning Christianity. Christian theologians use rational analysis and argument to understand, explain, test, critique, defend or promote Christianity.
Christian theology starts with the New Testament. Saint Paul, in his letters, and in his speeches in Acts of the Apostles, draws upon his training as a rabbi and on his experience of Christ starting outside Damascus to explain to Jews and Gentiles alike the meaning of the crucifixion and resurrection of Jesus. Throughout the History of Christianity later writers such as Luther and John Calvin have stressed the Bible as the cornerstone of theological understanding, although the Biblical canon itself is not without controversy. Catholic and Orthodox theologians have also stressed the importance of Church tradition for the faith. Thomas Aquinas and Saint Augustine are among the most important writers within the Roman Catholic Church.
Differences in theology have led to the many denominations within Christianity, starting with the separation of Jesus' followers from Judaism, and then particularly in the Great Schism and during the Reformation. After Luther's quarrel with the Pope, Reformed churches like the Lutherans and Baptists are established. Calvinism is very important within Protestantism, although the followers of Jacob Arminius do not accept it. Attempts at compromise in England between the Catholics and Puritans lead to the establishment of the Church of England.
Later movements include Methodism, Liberal Christianity, Pentecostalism, and Liberation theology.