This dissertation offers a holistic review of the so-called "Platonizing Sethian apocalypses" discovered, in Coptic translation, at Nag Hammadi, Egypt, in 1945. These texts are of fundamental importance to the history of philosophy and early Christian literature, for they played a major role in the conflict between the great Neoplatonic thinker Plotinus and Christian philosophers known to his circle in Rome, ca. 263 C.E. Recent scholarship has stressed the advanced metaphysics of these treatises, inviting speculation about their influence on Plotinus, and perhaps even Gnostic authorship for anonymous Neoplatonic treatises. More concretely, scholarship has almost universally assigned the Sethian texts to a "Pagan" provenance, due to a paucity of references to Scripture and their proximity to the famously Hellenic Neoplatonic schools.

This research neglects striking and crucial aspects of the treatises and has led to a fundamental misunderstanding of their doctrines. I demonstrate this in five chapters; the first two review background evidence. In chapter one, I discuss Neoplatonic evidence about Gnosticism, focusing on Plotinus' polemic. While cultural and eschatological issues are central objects of contention for him, scholars have paid little attention to their relevance for interpreting the Sethian treatises read by his opponents. Chapter two details the socio-historical background of Greek philosophical schools in the third century C.E., which was permeated with a politically and cultically conservative ideology articulated in Second Sophistic literature—and Plotinus.

Chapter three demonstrates that the Sethian texts themselves utterly reject this ideology. By employing the genre of "apocalypse" and making vigorous pseudepigraphic appeals to Judeo-Christian authoritative figures, they clearly attempt to appeal not to contemporary Hellenic schools, but readers invested in Biblical tradition. Chapter four reviews soteriological and eschatological passages in Sethian literature. Even the most sophisticated of these apocalypses are deeply invested in Sethian mythologoumena. Membership in the elect is circumscribed by the use of ethnic language, closely resembling contemporary Christian discourse about the new faith as a "race" separate from Hellenes and Jews and under the guidance of divine providence. Souls of the non-elect will be destroyed along with the world at the end of time—soteriological and cosmological positions unacceptable to Hellenic thinkers. Chapter five explores the foundation for the inter-confessional discourse between the Sethians and Plotinus, which appears to have been contemplative techniques. Other Sethian theurgic practices are entirely unrelated to Hellenic theurgy. Instead, they are indebted to contemporary Judeo-Christian practices known from Jewish apocalyptic literature and the Dead Sea Scrolls.

It is thus impossible that, however Neoplatonic their metaphysics, the Sethian Gnostic apocalypses of Nag Hammadi were composed by Hellenic intellectuals, or Gnostics attempting to appeal to a Hellenic audience. Instead, they appear to be "in-house" literature for Christian Gnostic thinkers, early representatives of advanced Christian Platonism, who should be classed with theological giants like Valentinus or Origen. Conversely, Sethianism's conflict with Plotinus marks the codification of Platonic thought as a cultically Greco-Roman enterprise, maintained by representatives of the school through its closing by the emperor Justinian.