Ennead VI.9: On the Good or the One, an early treatise, is placed by Plotinus’ editor at the very end of the Enneads, as the culmination of his thought, matching Plotinus’ own last recorded instruction, “to bring the god in you back to the god in the all.” It is a cosmological sketch, arguing that the being of anything depends on its being unified by its orientation to its own good, and so also the being of Everything, the All.

The One, or the Good, is at once the goal of all things both individually and collectively, and also the transcendent source of all that we experience, mediated through an intelligible order. But it is also, and perhaps more importantly, intended as a guide to the proper education and discipline of our own motives and experience. We are encouraged to put aside immediate sensory data, egoistic prejudice and sensual impulse, first to grasp at least a little of the intelligible order within which we all live, and at last to purge even those last intellectual attachments and experience what cannot be adequately described: the unity of being.

Plotinus was a Platonist, committed to expounding the doctrines put forward by Plato some seven centuries earlier. He was born and educated in Egypt, where he studied the teachings of Plato under the guidance of Ammonius Saccas. He came to Rome in 244 CE and built up a circle of followers devoted to studying Plato through Plato's own works and those of philosophers, both Platonist and non-Platonist, of the intervening centuries. From his fiftieth year Plotinus himself wrote down, in Greek, the findings of the seminars, and these writings were later edited by one of his pupils, Porphyry, and published in six groups of nine treatises entitled the Enneads (from the Greek word for nine – ennea).