The Hypostatic Union: Why the Incarnation of the Logos Does Not Involve the Whole Trinity

Since each Divine Hypostasis is only virtually distinct from the Divine Essence, and that Essence is identical with the Father and the Holy Ghost in exactly the sense in which it is identical with the Son, one might expect the Son’s Incarnation to entail the Incarnation of the Father and the Holy Ghost too. The following considerations remove the difficulty.

The Union Terminates in the Person, Not the Nature

It is an article of faith that the union of Godhead and manhood in Christ is strictly hypostatic — the Godhead is not united to the manhood immediately, nature to nature, but only mediately, through the Person of the Logos. Rusticus Diaconus puts it concisely: “It is not God the Word who is united to flesh through the divine nature, but the divine nature that is united to flesh through the Person of God the Word.”¹ Were the relation reversed — were Christ’s manhood united formally to the Logos’s nature rather than His Person — the result would be either an impossible commingling of natures or an equally impossible transformation of one into the other. So when we ask, regarding the term of the Incarnation, “Which of the Three Divine Persons became man?” the answer is: neither the Father nor the Holy Ghost, but the Son alone — “And the Word was made flesh” (John 1:14). Only the Sabellians and the Patripassianists ever denied this; every official creed and every early ecumenical council teaches it without exception.²

Durandus held that Christ’s manhood was united to the Logos primarily through an absolute attribute common to all three Persons — the Trinity’s shared self-existence — and only secondarily through the Logos’s own personality.³ This does not match the Church’s teaching, since it would make the Incarnation primarily an incarnation of the whole Trinity, and only secondarily of the Son. The Sixth Council of Toledo (A.D. 675) implicitly rules this out: “The whole Trinity is to be believed to have worked the Incarnation of this Son of God [as efficient cause], since the works of the Trinity [toward creation] are inseparable. Yet the Son alone took the form of a servant in the singularity of His Person [as the term of that act], not in the unity of the divine nature — in what is proper to the Son, not in what is common to the Trinity.”⁴

Efficient Cause vs. Term of the Union

Considered actively, as an external work of God, the Incarnation — though specially appropriated to the Holy Ghost in devotional language (“conceived of the Holy Ghost”) — has as its efficient cause the entire Trinity, or the Divine Essence as such.⁵ The Three Divine Persons together created Christ’s manhood, preserve it in being and action, and concur in all its creaturely operations. And just as the Incarnate Word remains immanent in the Father and the Holy Ghost by the Trinitarian perichoresis, so the Father and the Holy Ghost are present in Christ by virtue of the Hypostatic Union — a presence surpassing even God’s ordinary omnipresence in creatures or His special indwelling in the souls of the just; a unique kind of immanence in its own right.⁶ “I and the Father are one… The Father is in me, and I in the Father” (John 10:30, 38); “He that seeth me seeth the Father also… Do you not believe that I am in the Father, and the Father in me?” (John 14:9-10).

Three Speculative Puzzles

Theologians customarily raise a further question here: could the Father or the Holy Ghost have become man instead of the Son? St. Anselm seems to deny it, on the ground that either alternative would create hopeless confusion in the use of the term “Son” — had the Father become man, He would have had to appear as “son of man,” which clashes with His personal character as Father, and likewise for the Holy Ghost.⁷ The Schoolmen generally preferred St. Thomas’s solution: the Father and the Holy Ghost could have become incarnate just as the Son did, since “the temporal filiation by which Christ is called ‘son of man’ does not constitute His Person the way His eternal filiation does; it is merely a consequence of His temporal birth. So if the name ‘filiation’ were transferred to the Father or the Holy Ghost in this same [temporal] sense, no confusion of Persons would follow.”⁸

A harder version of the question: could all Three Divine Persons together become incarnate in a single human nature, such that this one human nature would be a threefold Divine Person — Father, Son, and Holy Ghost all at once? This is not the Sabellian absurdity of asking whether the Father is the Son; it asks instead whether the Three Persons could assume one and the same human nature as three separate and distinct Hypostases. St. Bonaventure thought this “could be reasonably defended”;⁹ the later Scotists held it involves an intrinsic contradiction. St. Thomas resolved it on the principle that “as the Three Divine Persons can, without contradiction, subsist in one Divine Nature, so they can also subsist in one human nature.”¹⁰

A still harder question: could the Logos assume one or more additional human natures, simultaneously or successively, beyond the one He already has — becoming incarnate repeatedly, say, on different worlds? Given what has already been established about the infinite scope of a Divine Hypostasis, the answer must be yes: to claim a Divine Person could assume only one human nature would be to deny God’s omnipotence and infinity. As St. Thomas teaches: “The power of a divine Person is infinite, and cannot be limited to anything created. Hence it must not be said that a divine Person has so assumed one human nature that it could not [simultaneously] assume another. For it would seem to follow from this that the personality of the divine nature was so exhausted by one human nature that no other could be assumed into it — which is impossible.”¹¹ “It belongs to the very condition of the divine Persons that one of them does not exclude another from sharing the same nature, but only from sharing the same Person… It is therefore not impossible for two or three of the divine Persons to assume one human nature.”¹²

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