Plotinus (205-270) was the founder of Neoplatonism. He didn’t just revive Plato’s ideas; he revamped them and combined them with those of Pythagorus. The result is a dualism that contends that the soul and body are completely separate.
Little is known of the childhood and origins of Plotinus. He was said to have been born in Egypt but the exact location is unknown. At 28, he went to Alexandria to study philosophy. In 245, Plotinus moved to Rome. In that same year, Norway was building the last of its sewn boats (sewing was soon to be replaced by iron nails), China invaded what is now South Korea, and both St Nicholas and the Roman Emperor Diocletian were born.
Plotinus coined an illumination metaphor that survived for hundred of years and was used by Descartes. He said the mind is like an eye: it can see truth but only when it is illuminated by God (nous). But God was not the man-God of Christianity or the special revelation of secret knowledge the Gnostics sought. For Plotinus, nous was the essence of eternal, spiritual intelligence and can only be detected by the soul. Everything flows from the central, eternal unity of nous and forms a hierarchy of truth. The soul (psyche), which is derived from nous, emanates to the real world (physis). In this integrated system, then, God is an intellectual unifying construct and is a part of all nature. And truth comes from the spiritual (nous) to the mental (psyche) to the physical (physis).
Plotinus was opposed to Gnosticism because it seemed irrational and presumptuous. He undoubtedly would have held a similar opinion of Christianity or other religions. For Plotinus, the essence of religion was the mystical union one achieves with universal truth. Anything un-Greek just wouldn’t do.
Although not a Christian, Plotinus influenced their view of the soul. Prior to Plotinus, Christians has accepted a more integrated view of body-soul, comparable to that of Jewish traditions. After Plotinus, the soul was thought of as separate from the body. Interestingly, Plotinus would not have conceived of reuniting the soul and body after death but Christian thought clearly teaches such a reunification.
For more on this topic, here’s a video on the Mind-Body Problem.