The essential point of this book is to demonstrate that a crucial element of Plotinus’s thought—his conception of mystical union with the One—cannot be understood solely within the conventional history of philosophy, or as the product of a unique, sui generis psychological propensity, but rather must be reconceptualized in the broader context of contemporaneous Gnostic thought and praxis. The conclusion is that Plotinus tacitly patterned his mystical ascent to the One on a type of visionary ascent ritual that is first attested in Gnostic sources. These sources include the Platonizing Sethian tractates Zostrianos (NHC VIII,1) and Allogenes (NHC XI,3) of which we have Coptic translations from Nag Hammadi and whose Greek Vorlagen were known to have been read in Plotinus’s school.
The argument has three essential components: First,  Plotinus’s ascent towards union involves a contemplative reversion upon the “center-point” of the self, which is, in effect, a hypernoetic and hyperontic aspect of the supreme principle—the One—that abides within the human subject. At the penultimate moment, just prior to the ultimate union or coalescence with the supreme principle, Plotinus describes an experience of a sudden, luminous vision of this transcendental self.  This momentary self-apprehension deliberately recapitulates the first eternal moments of ontogenesis, in which the prenoetic efflux from the One reverts to its source—its former self—to acquire delimitation and independent subsistence as hypostatic Being-Intellect. In fact, Plotinus considers these two moments of self-apprehension—the one mystical, the other primordial—to be homologous or even identical, and he believes the transcendental principle within the self to be consubstantial with the prenoetic efflux of the One. Finally,  a very similar schema—one that identifies the primordial and mystical moments of self-apprehension—is prominent, and in many ways more explicit, in the Coptic versions of the Platonizing Sethian ascent tractates whose Greek antecedents were read and critiqued in Plotinus’s circle (as well as in related Platonizing Sethian treatises), and in earlier, “classic” Sethian, Hermetic, and Valentinian literature). The Sethian tractates describe an ascent through the complex metaphysical armature mediating between the cosmos and the unknowable, transcendent deity. As in Plotinus, the Sethian aspirant undertakes a mystical self-reversion and experiences a moment of self-apprehension during the final stages of the ascent; this is explicitly described as a residual, indwelling imprint of the reflexive self-manifestation of the transcendent deity during the first eternal moment of ontogenesis. Despite their different approaches and much-discussed philosophical disagreements, the resemblance between Plotinus’s mysticism and these Gnostic comparanda are too robust to be coincidental, and suggest that Plotinus developed his own mysticism in close dialogue with contemporaneous Gnostics. This conclusion suggests that we must reconceptualize the nature of the relationship between sectarian praxis and academic philosophy in late antiquity, and accord to the former a far greater agency than is usually assumed.