Western philosophy has been in the throws of dualism since Plato first expounded the idea that reality as we normally perceive it is an illusion (or, at least, illusory) and that the true Reality lies in the unchanging and perfect realm of the forms, which are unattainable to mere mortals. The form of our relationship to this dualism has shifted over the ages, from Plato praising the soul who sought to attain this unattainable realm to Kant sort of shrugging off the noumenal as a sort of thought construct necessary to preserve human freedom from the apparent grind of experiential determinism. Back and forth the pendulum swings, first to the ethereal and (apparently?) imaginary world of The Good and the spiritual, back to the dirty and roiling world of day-to-day experience where power rules all and conceptions of anything higher are either muddled or deemed unnecessary.
This dialectical tension reminds us of a philosophical question which reaches back even further than Plato, though Plato was well aware of the question: the question of "The One and The Many". Is truth a unitive concept, always and ever the same, or is it a multitude, as permeable and malleable as wind-blown sands? To answer "The One" seems to destroy human freedom (which our very souls rebel against, for to say this is to destroy the efficacy of the soul who asks the question), to answer "The Many" appears to destroy the possibility of Goodness and Truth (and again, our soul's rebel, for to say this is to destroy the very category of the question that attains such an answer). Neither option is really possible for us to take seriously as "The Truth" for all time, and so our philosophers look to subtle logical constructs and distinctions to balance the one claim against the other.
The obvious answer is that neither answer is fit for the soul of a human being. So are we to ignore the question, and merely get on with our existence un-examined? No, for such a stance also destroys the human soul, whose glory is to discover those things that are hidden. The only possible answer (to jump ahead a few steps, if we may be allowed to be so bold) is that Truth is both One and Many (or, at least, One and A Few). And because we affirm the both/and rather than the either/or the very dualism that first seduced the Western Mind must be destroyed for the useless idol that it is. Thus Spirit and The Forms are not (at least from the perspective of humanity) ontologically separate from body and matter. Existence is suffused with Spirit just as existence flows upwards towards Spirit and gains eternal significance--though, they are ever so far apart as we now are, ever so far apart. So far apart that an eternity of time and space lies in between them, a swirling chasm of darkness into which a great evil has crept out of the primordial cauldron.
Dualism in this model speaks more to the fraught and ontologically unsustainable condition of the now-existent physical world then it does to "Truth" in any absolute sense. If it is the "Truth" it is the truth of a fallen humanity untouched by grace, or unwilling and unable to acknowledge that grace which serves to bridge such an unbridgeable chasm, and make right the division running through the center of the human heart.