Plotinus The Enneads -

The absolute, simple, and transcendent first principle. It is beyond "being" and "intellect," acting as the source of all existence.

Each layer of reality becomes less unified and more complex as it moves further from the One. PLOTINUS THE ENNEADS

We return to the One not by traveling, but by turning our attention inward, away from bodily desires and toward our own intellect. The absolute, simple, and transcendent first principle