Andrew Wilson writes: Is the second person of the Trinity omnipresent and incarnate at the same time? Is the Son of God both asleep in a manger, or a boat, or even dead, while he is also filling all things and sustaining the universe? The so-called extra Calvinisticum gives a confident yes—and the Reformed view of the Lord’s Supper depends on it, among other things—but it feels counter-intuitive and obscure to us nevertheless. So here’s a wonderfully helpful illustration from Gavin Ortlund’s excellent new book, Theological Retrieval for Evangelicals. It’s one of the best illustrations I’ve heard in years, and it pretty much sums up what theological teaching ought to be.

Suppose, just as Christ comes into his own creation at the incarnation, Tolkien had written himself into Middle-earth as a character of the story alongside Frodo and Merry and Pippin and the rest. Had Tolkien done so, he would not for that reason cease to exist in Oxford (in fact, his whole existence in Middle-earth depends on his continued writing). Nor has the unity of Tolkien’s person been impaired, for one person can simultaneously be in Middle-earth and Oxford, because they are not two different “places” within one realm but two different realms altogether. In other words, it is one thing to be in Oxford and Cambridge at the same time, but another thing to be in the Shire and Oxford at the same time; and the relation of “heaven” and “earth,” and with it the relation of Christ’s divine and human natures, is more like the relationship between the Shire and Oxford. This is the value of the metaphor of story—the distinction between “author” and “story” is robust enough to retain two natures while fluid enough to retain one person. Middle-earth and Oxford may be two while Tolkien remains one …

It is not merely that Tolkien is not confined to the body of his incarnate character in Middle-earth; that is true, but that is just about the least significant thing one can say about him. Supposing the incarnated Tolkien is sitting in Frodo’s home in the Shire for a meal; this does not in the least hinder the Tolkien in Oxford from going to sleep, or traveling to India, or putting the book down for twenty years. His incarnate existence in Middle-earth does not diminish him in the least or even distract him. He is not merely extra but completely and fully extra. In other words, it is not that he reduces himself to an incarnate life but leaves a tiny bit left over that is not exhausted by his incarnation; rather, that which is extra continues on without the slightest downgrade or even interruption during the incarnation.

This is what theological teaching should be. It is creative faithfulness: finding new ways to say old things. It is beautiful orthodoxy. If you’re wired this way, the whole book is worth reading.