Michael agrees with Butler. “To choose what I must be is mine.” In other words, he will decide to maintain himself post-corpse by performing correctly “the deeds which we have done in the body.” He suggests obstacles to the easy achievement of those deeds, citing “this feeble frame, | For ever racked with ailments fresh” but in the next stanza he reveals that those problems have been introduced so that they can be argued into smaller importance. “This is not I.” (“I” at some points in the poem is neither the physical body nor the personality – since the personality can be estranged from it – but I think this is the fault of semantics rather than metaphysics.)
Geoffrey Hill, in his Tanner lectures, has another point of view, different but likewise rooted in a Christianised culture: “the nature that is most intimately mine” (which I believe corresponds to Michael's notion of “personality”) is necessarily penetrated and corrupt; it is not so free of its physical existence.
My language is in me and is me; even as I, inescapably, am a minuscule part of the general semantics of the nation; and as the nature of the State has involved itself in the nature that is most intimately mine.
If it is “intimately mine” then the simple solution that Michael proposes in his poem – when you discard the body in death you are discarding everything that isn't you – is being questioned. But it depends. How intimate is Hill's intimately? How intimate do you want it to be? To get rid of that question you could say, “Not as intimate as that.”
If Michael, static in the afterlife, has discovered that he was right, then is he reading Hill's oeuvre -- which has been in a condition of struggle from the first line of the first poem in his first published book -- and muttering, “Geoff, Geoff, what a waste of time”?