It seems to me that as relativity is to quantum physics, so the metaphysics of pluralism is to monism.
These are two different, basic ways of looking at the world. Thus relativity cannot be integrated with quantum physics, the particle theory of light cannot be integrated with the wave theory of light, and pluralist theology cannot be integrated with monist.
If Einstein was perhaps the most creatively inspired scientist who ever lived, then the fact that he regarded quantum physics (which he helped to found) as fundamentally wrong, ought to be of significance - significant in the sense that Einstein recognized that quantum physics was simply based on a fundamentally different set of assumptions - and one which he regarded as alien to his basic understanding of how things work.
General Relativity is based-in, extrapolated-from, a metaphysical world that is common sense, real world, normal logic: a world where time is linear and sequential, where you get nothing from nothing, where causality is understood like bouncing billiard balls and where all interaction is constrained by the maximum possible speed of even the tiniest and fastest billiard ball: the speed of light.
Relativity can be, and is,explained by 'thought experiments' such as 'riding on a beam of light' - apparently Einstein used these thought experiments to discover the theory. Quantum physics cannot be explained by thought experiments - and what you get from an attempted quantum thought experiment such as Schrodinger's cat is the fact that quantum physics cannot be explained by thought experiments!
Quantum physics is a world outwith common sense and human experience: where you can get something from nothing, where time may not be linear nor sequential, where there may be instantaneous interaction regardless of distance, and things can-and-cannot be simultaneously.
Ultimately, quantum physics is a world of equations - of formal models - it is not a human world, it is utterly non-commonsensical.
General relativity and quantum theory cannot both be true, because at a metaphysical level they inhabit different universes. Both could be wrong, but only one can be true - with the other an un-grounded, ad hoc set of assumptions which happen to be useful for particular tasks.
In theology somewhat likewise. Pluralism is based in common sense and everyday mechanisms of pragmatic causality; monism is based in a world of absolute theory.
This best comes out in relation to time. For pluralists, time is what it seems to be - linear and sequential; for monism, time can stop, be reversed... all sorts.
In fact, monists do not regard time as a constraint - since time is neither linear nor sequential, time can - in practice, time can be fitted-around other - more important, more fundamental - things.
Pluralism is ultimately materialist and there is one kind of stuff. Causality is direct - one thing causes another because in bangs-into the other. There can be no causality without physical interaction, which takes time - and time cannot be reversed. There is no communication which does not take time.
Monism sees all kind of interactions, and things different in kind. Monism may posit immaterial things, causality without substance - so causality may be instant over all of space: there may be action at a distance without any time elapsing. There is no before nor after - so the future may cause the past.
Pluralism and monism cannot both be true, because at a
metaphysical level they inhabit different universes: either everything has one ultimate cause, or more-than-one ultimate cause.
Both could be
wrong, but only one can be true - with the other an un-grounded, ad hoc set of assumptions which happen to be useful for particular tasks.
In religion, when it comes to the soul, a pluralist imagines it as a kind of stuff; a monist may regard the soul as immaterial. Same with consciousness. Same with the Holy Ghost.
A pluralist necessarily regards God as material - because everything real is material; a monist can posit a God that is everything - all things; a God that is 'nothing' no-thing (in the sense of having no substance, material or stuff.
A pluralist supposes God to do things in broadly the same kind of way that humans do things: by one thing causing another over time, by taking pre-existing material and shaping it - all extrapolated to happen vastly accelerated and vastly larger in scope; but a monist regards God as working by entirely other means: making something from nothing, making many things happen instantly, making things happen simultaneously without any specific communication between them, whatever...
A pluralist regards God as broadly being of the same kind as Man - as a personage - having a character: a God of passions, emotions, feelings, intentions, desires, motivations - God as linearly and continuously linked to Man and inhabiting the same reality; but a monist regards God as utterly different from Man, inhabiting a different reality, qualitatively different, utterly incomprehensible, fundamentally unknowable, unpredictable, of a nature so other-than Man that it is ridiculous, childish, blasphemous to talk of God being a person or having passions, emotions, intentions etc.
The pluralist regards God as having a morality, the monist regards God as being morality.
And so on.
From all this it can be seen that Christians, trinitarians, have a tough job - probably an impossible job - in creating an adequate philosophy of Christianity; since necessary features and properties lie on both sides of the pluralism-monism divide; and this divide cannot be mended any more than relativity can be integrated with quantum physics.
My conclusion is that deep metaphysical coherence is unattainable in Christianity.
Christians must not get 'hung up' on philosophy.
Of course, most don't - but intellectuals, including theologians, certainly have done and continue to do.