The claim that the LORD is eternal in the sense that in his life—in the life he is, in the Trinity he is—there is no division according to timespace is among orthodoxy’s key elements because it is ingredient to the proper drawing of the distinction between the LORD and the ensemble of creatures that is the world; their temporality is a constituent element of their creaturehood, providing the framework and horizon of the modes of their relation to the LORD. Were the LORD also to be temporal, subject to change, then temporality would not be a constituent of creaturehood—a mode under which creatures relate to the LORD—but would instead be a horizon within which both the LORD and creatures are found. That is one way to misrepresent the LORD by replacing him with an idol.
Another way to put this view of the LORD is to say that he is an atemporal state of affairs of vast internal complexity. This complexity is given by the fact that he is triune: the three persons of the Trinity are related one to another in many more ways than those specified by the language of the creeds, but those relations are all, first, last, and always, relations of love. The persons are lovers, eternally and intimately intertwined; the baroque complexity and variety of human loves, sexual and other, is a pale reflection of and participation in the divine loves that are the LORD. Mathematics is another window into the range and depth of the complexity of the atemporal state of affairs that is the LORD. The relations that obtain eternally among such abstract objects as numbers and sets are infinite, and accessible only in part to human intellects. Such relations are, in respect of atemporality and complexity, like the inner-Trinitarian relations. Of course, there are respects in which mathematical and inner-Trinitarian relations differ profoundly; but in these ways they are importantly alike, and it is probable that the best account to give of this likeness is one that understands mathematical objects to subsist in the LORD.
The LORD’s eternality is unique to him: eternity is constituted by the divine Trinity, and since everything that exists other than the LORD is a creature and belongs to the created order, whose distinctive feature is that it is temporal, it can belong only to him … Anything that is eternal—and only the LORD is eternal—lacks a temporal beginning, a temporal end, and any succession or alteration. He exists all at once, semper eodem, “always the same,” changelessly … Understanding the LORD’s life, his life as the Trinity he is, as happening tota simul means that there is no succession in that life, no before and after. Every event in that life is simultaneous with every other, though even that way of putting it disposes creatures for the time being such as ourselves to think this means that there can be no separation in the events that constitute the LORD’s life, that because they are not differentiable by appeal to timespace they are not differentiable at all because that is the only way in which events can be differentiable. It is true in the spatio-temporal order that identity in timespace means identity simpliciter. If one creature or state of affairs is here-now, and another is also, and identically, here-now—or, to put the same point differently, if two creatures or states of affairs have exactly the same spatio-temporal coordinates—then this just means that they are the same creature. They occupy the same timespace. We might think, following this pattern of reasoning, that if the LORD’s life is tota simul, then this must mean that it is self-identical, without any real distinctions of differentiations. And that is one part of the intuition behind the idea of the LORD’s simplicity.
But simplicity (and eternality) do not rule out every kind of differentiation or distinction. They deny only those kinds that suggest composition, and thereby the possibility of division. Differentiations such as those that relate the persons of the Trinity one to another need not do this, and that is because those relations (begetting, proceeding, and so on) conjointly constitute the LORD, making him, as Augustine likes to say, the trinitas quae deus est—the Trinity that God is. It is not that the LORD is a being who has those relations; it is that those relations, taken together, exhaustively constitute the simplex Dominus, the LORD who is simple. That the LORD is triune, however, does mean that his eternity is not that of an extended spatio-temporal period, like, in definition, a Euclidean point. It is, rather—and here we have to use metaphors—an extended but not compounded all-at-onceness, an enduring, but not spatio-temporally enduring, present.
This extended all-at-onceness is what the LORD’s eternity is. Temporality, by contrast, is everything that this is not. It (temporality) is the life of the fallen world, and, though differently, of the prelapsum cosmos, and of heaven. By analogy with the LORD’s eternity, which just is the set of relations that makes the three persons he is what they severally are, the world’s temporality just is the set of relations creatures bear to one another. These relations are what makes the world what it is, spatio-temporally speaking, and they are all at least (if not only) spatio-temporal relations, each construable through the categories “before,” “after,” and “simultaneous with.” Every creature, every ensemble of creatures, and every state of affairs is temporal in the sense that it bears an enormous number of relations of this kind to other such creatures. The temporal order as a whole, timespace properly considered, just is this set of relations, and all of them perdure.