This session explored major heresies in the early church—such as Gnosticism, Marcionism, and Arianism—which distorted the nature of Christ, Scripture, and salvation, prompting theological responses like the Council of Nicaea (325 AD) that affirmed Jesus as fully divine and of the same substance as the Father. It also examined how Constantine’s legalization of Christianity transformed the church’s structure and culture, leading to widespread growth, nominal conversions, clerical privilege, and eventually the rise of ascetic movements like the anchorites and stylites. These developments marked the end of the early church era and the beginning of new theological and ecclesial challenges.