Proto-orthodox Christianity in the context of Christianity in the 3rd century

Gnosticism (from Ancient Greek γνωστικός (gnōstikós) 'having knowledge'; Koine Greek: [ɣnostiˈkos]) is a collection of religious and philosophical ideas and systems that coalesced in the late first century AD among sects of early Christianity and other faiths. It is not a singular, homogeneous tradition or religion, but an umbrella term used by modern scholars to describe different groups and beliefs that shared certain characteristics. These diverse Gnostic groups generally emphasized personal spiritual knowledge (gnosis) above the authority, traditions, and proto-orthodox teachings of organized religious institutions. The Gnostic worldview typically distinguished between a hidden, uncorrupted supreme being and a flawed demiurge responsible for creating material reality. Gnostics held this material existence to be evil and believed the principal element of salvation was direct knowledge of the supreme divinity, attained via mystical or esoteric insight. Many Gnostic texts deal not in concepts of sin and repentance, but with illusion and enlightenment.

Although the exact origins of Gnosticism cannot be traced, Gnostic writings flourished among certain Christian groups in the Mediterranean during the second century. In the Gnostic Christian tradition, Christ was seen as a divine being that had taken human form in order to lead humanity back to recognition of its own divine nature. Judean–Israelite Gnosticism, including the Mandaeans and Elkesaites, blended Jewish-Christian ideas with Gnostic beliefs focused on baptism and the cosmic struggle between light and darkness. Syriac–Egyptian groups like Sethianism and Valentinianism combined Platonic philosophy and Christian themes, seeing the material world as flawed but not wholly evil. Other traditions include the Basilideans, Marcionites, and Thomasines. Manichaeism, which adopted Gnostic concepts such as cosmic dualism, emerged as a major religious movement in the third century, briefly rivaling Christianity.

Pauline Christianity or Pauline theology (also Paulism or Paulanity), otherwise referred to as Gentile Christianity, is the theology and form of Christianity which developed from the beliefs and doctrines espoused by the Hellenistic-Jewish Apostle Paul through his writings and those New Testament writings traditionally attributed to him. Paul's beliefs had some overlap with Jewish Christianity, but they deviated from this Jewish Christianity in their emphasis on inclusion of the Gentiles into God's New Covenant and in his rejection of circumcision as an unnecessary token of upholding the Mosaic Law.

Proto-orthodox Christianity, which is rooted in the first centuries of the history of Christianity, relies heavily on Pauline theology and beliefs and considers them to be amplifications and explanations of the teachings of Jesus. Since the 18th century, a number of scholars have proposed that Paul's writings contain teachings that are different from the original teachings of Jesus and those of the earliest Jewish Christians, as documented in the canonical gospels, early Acts, and the rest of the New Testament, such as the Epistle of James, though there has been increasing acceptance of Paul as a fundamentally Jewish figure in line with the original disciples in Jerusalem over past misinterpretations, manifested through movements like "Paul Within Judaism".

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.