The document discusses the rise and spread of Christianity from a small sect within Judaism in the first century CE to a dominant world religion. It covers key figures in Christianity such as Paul, who established churches in major cities from the 1st-3rd centuries CE and Tertullian who viewed the church as a counter-kingdom to the Roman Empire. The document also discusses divisions within Christianity between Catholic, Orthodox, and Protestant traditions and how figures like Martin Luther and John Calvin shaped Protestantism.