What a wonderful essay, logos!
The only historical figure I can think of who actually tried to live the way Christ did -- in itinerant ministry -- was Francis of Assisi. He chose a life of total poverty, relying solely on the Lord for his daily bread, and a place to lay his head down to sleep at the end of the day. Only in this way, Francis believed, could he truly live a life in imitation of Christ. Obviously, there are few takers for this sort of thing. Very few people would choose a life like this -- with the possible exception of "street people." (I.e., the "homeless," many of whom have mental disabilities and substance abuse problems....)
I don't think we can blame Plato for the dualism of human life. His was a "cosmology of wholeness." He recognized that man was "part beast, and part divine" -- but sees the parts as complementary, and in their dynamic relations as constituting one whole -- Man. This model suggests that man actually does live both in time and in Eternity. I'm not sure, however, that Plato would see this as an instance of "duality." The material world is "in time"; but the spiritual world -- the divine -- is eternal; and man incorporates both within himself.
The symbol that comes to mind is the Christian Cross. The vertical is the timeless projection of the soul, from its ground in the cosmos -- which I also imagine to partake of the divine, since it is an expression of divine creative will -- to its search of the divine Beyond whose great symbol, for Plato, was the Agathon. (This not God Himself, but the vision of divine perfection and goodness.) For man, both "ends" stretch virtually without limit beyond man's ability to perceive them; but man's inner life is experienced as a tension between the two "pulls."
The horizontal of the Cross, running perpendicular to the vertical: This is the line of time.
In the vertical axis, time past, present, and future are simultaneous -- thus "timelessness" is the nature of the soul, psyche. This has been referred to as the Eternal Now. On the horizontal, time is linear, sequential, and unidirectional. This is the line that people spontaneously see, for its deals with past, present, and future -- and the last is of great concern to most men, both inside and outside the meaning you give, as an expectation of a "future heaven."
But actually, "heaven" is already "in us" -- along the vertical line. Few people notice this, however.
Which is why I've speculated that Hell is not necessarily a future possibility only. We can have living Hells -- which would result from the "poor order of the psyche" (which I interpret as lack of conformance with "the laws of Nature and of Nature's God" as a famous secularist once put it), running along the vertical line.
Of course, poor order there is inevitably played out along the horizontal time line. It is a translation of psychic disorder into the empirical realm, both personal and social.
I have to leave it there for now, logos, and get back to work!
Thank you so very much for your beautiful essay!