... the holy writers would never have ascribed the creation unto more than one, unless that one in some sense or other had been more than so. Wherefore, they do not change, as is pretended, the plural expression into a singular; but the Holy Ghost, expressing the same thing, of making man in the image of God, sometimes expresseth it in the singular number, by reason of the singularity of the nature of God, which is the original of all divine operations, for God works by his nature; and sometimes in the plural, because of the plurality of persons in that nature ... because his nature is one and singular, but subsisting in more persons than one ...
It is important to note that throughout this chapter, "God" refers to the divine essence or nature:
Wherefore the visible works of God, man only excepted, were designed for no other end but to declare in general the nature, being, and existence of God. But in this nature there are three persons distinctly subsisting; and herein consists the most incomprehensible and sublime perfection of the divine being.
How numeric unity views the relationship between the persons of the Trinity and the one divine nature as coherent is a mystery, for it seems they must either admit the person are merely parts of God or that the persons are separate, self-existent Gods (autotheos). By referring to the persons as subsisting "in" the "one divine nature" "equally" and recalling his true remarks on eternal generation in my last post, Owen appears to have implicitly opted for the former:
But whereas creation is a work proceeding from and an effect of the infinite properties of the one divine nature, our Creator is but one, although that one be equally Father, Son, and Spirit.
The divine nature, then, becomes a sort of supra-Person in whom the persons subsist and who subsists in the persons, a sort of disfigured perichoresis wherein it is hard to avoid the idea that the persons become merely modes of operation for the divine nature:
God doth not here speak unto others that are not himself, but by speaking as he doth, he declares himself to exist in a plurality of persons, capable of mutual consultation and joint operation ... For we say not that God speaks unto others besides himself, nor calls in others to the work of creation; but God alone speaks in himself and to himself, because as he is one in essence, so as to personal subsistence there are three in one, as many other places of the Scripture do testify. And these three are each of them intelligent operators, though all working by that nature, which is one, and common to or in them all.
This is the inevitable effect of making the seemingly simple but remarkably damaging mistake of referring the divine nature abstracted from and as the subject of propositions about the persons of whom it ought to be predicated:
Man was peculiarly created unto the glory of the Trinity, or of God as three in one.