Is this you or are you quoting somebody?
Regardless its pretty much nonsense so far as Aristotelianism/Thomism is concerned.
"Death is the separation of body and soul, the destruction of a full human being.
In a loose analogical sense we might say the soul may be “dead” (as in a state of mortal sin) in so far as a soul deprived of SG can do nothing of itself to merit any more grace and so is “dead” re Communion with God (just as the Communion of the body with the soul is destroyed at death).
However this is not really what you are saying above.
You seem to say “the soul is dead without sanctifying grace because the soul is immaterial (and eternal).”
That just makes no sequitorial sense at all.
And the difficulty with T&M’s approach is that he seems to believe “human being” is defined not just by “union of body and soul” but rather by “union of body, soul and grace”.
Thus if God through original sin deprives the innocent of grace he is somehow being unjust and depriving them of something He intrinsically committed to providing naturally by bringing them into existence.
The problem with this is, of course, that such a definition of what it means to be a “human being” is at odds with the very definition of “grace” as a free gift (that is what grace means) that is not owed by God at all.
Its like trying to say that an irresistible force should be able to budge an immovable object…what the

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Agreed in the sense as above.
Though there is another sense of “natural” in so far as had A&E not sinned their progeny would “naturally” have been born with SG - as a free yet certain gift from God.