Irenaeus of Lyons in the context of "Original sin"

The term "Great Church" (Latin: ecclesia magna) is used in the historiography of early Christianity to mean the period of about 180 to 313, between that of primitive Christianity and that of the legalization of the Christian religion in the Roman Empire, corresponding closely to what is called the Ante-Nicene Period. "It has rightly been called the period of the Great Church, in view of its numerical growth, its constitutional development and its intense theological activity."

The Great Church, also called the catholic (i.e., universal) Church, has been defined also as meaning "the Church as defended by such as Ignatius of Antioch, Irenaeus of Lyons, Cyprian of Carthage, and Origen of Alexandria and characterized as possessing a single teaching and communion over and against the division of the sects, e.g., gnosticism, and the heresies".

Papias (Greek: Παπίας) was a Greek Apostolic Father, Bishop of Hierapolis (modern Pamukkale, Turkey), and author who lived c. 60 – c. 130 AD. He wrote the Exposition of the Sayings of the Lord (Greek: Λογίων Κυριακῶν Ἐξήγησις) in five books. This work, which is lost apart from brief excerpts in the works of Irenaeus of Lyons (c. 180) and Eusebius of Caesarea (c. 320), is an important early source on Christian oral tradition and especially on the origins of the canonical Gospels.

Valentinianism was one of the major Gnostic Christian movements. Founded by Valentinus (b. c. 100 CE – d. c. 165 CE) in the 2nd century, its influence spread widely, not just within the Roman Empire but also from northwest Africa to Egypt through to Asia Minor and Syria in the east. Later in the movement's history, it broke into Eastern and a Western schools. The Valentinian movement remained active until the 4th century, declining after Emperor Theodosius I issued the Edict of Thessalonica in 380, which established Nicene Christianity as the state religion of the Roman Empire.

No evidence exists that Valentinus was labeled a heretic during his lifetime. Irenaeus of Lyons, who was the first patristic source to describe Valentinus's teachings—though likely incompletely and with a bias toward the time's proto-orthodox Christianity—did not finish his apologetic work Against Heresies until the latter 2nd century, likely sometime after Valentinus's death. The rapid growth of the Valentinian Gnostic movement—named eponymously after Valentinus—after his death prompted early Christian thought leaders, such as Irenaeus and later Hippolytus of Rome, to write apologetic works against Valentinus and Valentinianism, which conflicted with proto-orthodox theology. Because the proto-orthodox camp's leadership encouraged the destruction of Gnostic texts writ large, most textual evidence regarding Valentinian theology and practice comes from its critics—particularly Irenaeus, who was highly focused on refuting Valentinianism.