What happened was that at the incarnation, while continuing to exist eternally in the form of God, He added to that by taking the form of a servant.
— J. N. D. Kelly —

 Given the importance of the extra in historical theology, it is surprising how quickly it is rejected or replaced with something else. The extra is crucial in helping the church to explain the full scope of the Scriptural presentation of the incarnation and how the Son functioned in and through both natures,
— Stephen J. Wellum —

At Christmas we celebrate the birth of baby Jesus. And with candles glowing and carols singing, we draw near to the babe born of Mary and celebrate the fact that God is with us—Immanuel.

At the same time, when we celebrate Christ’s condescension, there can arise a significant misunderstanding about Christ’s humanity. In song, as well as sermon, we find lyrics that describe Jesus “leaving heaven,” or not knowing about why he is coming to earth—“Baby Jesus, do you know you will die for our sins?”  These boilerplate Christmas tag lines, but are they true? Do they faithfully represent the miracle of the Incarnation?

On the surface, they may sound fine. They praise God for Christ’s birth and his sacrificial mission to bring salvation. Yet, when we probe more deeply, it becomes apparent lyrics like these and many unchecked thoughts about the birth of Christ assume beliefs that have often been described as heretical in church history.

In particular, Christmas has a way of unwrapping the kenotic heresy—the belief that when Jesus emptied himself (ekenōsen) and became a man,  he also left many (or all) of his divine attributes behind. The theory, expressed in many ways, asserts that for the Son of God to become human, he must set aside his omniscience, his omnipotence, and his omnipresence. After all, true humanity does not uphold the universe, right?! For Jesus to be fully human then, his humanity must be fixed in one place, ignorant of many things, and unable to do all the things that God does.

How this will be preached, sung, or believed will differ from person to person and tradition to tradition. But what seems to be missing in many (evangelical) Christmas celebrations is an appreciation for the fact that when Christ emptied himself, he did so by addition and not subtraction. As Philippians 2:7 tells us, Christ “emptied himself, by taking the form of a servant, being born in the likeness of men.” The Son of God did not become a man by denying his deity, but by adding humanity (a full human nature, that is) to his divine sonship. He veiled his glory in the Incarnation; he did not lose it!

Such an addition of a human nature to the Son’s divine nature is the definition of the Incarnation. In fact, throughout church history a proper understanding of Christ’s two natures has been a bedrock for orthodox Christology. And in particular, a doctrine known as the extra Calvinisticum—or better, the extra Catholicum, because Calvin didn’t invent it—has been a staple of explaining how the Son of God remains wholly, fully, and glorious divine even as he assumed a humanity that was and forever will be wholly, fully, and entirely human.

To flesh out what the Incarnation means for the Son of God, let me share a number of reflections from church history that capture the glorious truth that the Son of God born in Bethlehem is simultaneously the Lord of glory upholding the universe. This is what the extra Calvinisticum affirms and it is worth our reflection as we celebrate the birth of Christ.

Celebrating Christ’s Birth with ‘Extra’ Care

In his outstanding work, The Son of God Incarnate, Stephen Wellum provides a short history of this doctrine and the way it has helped Christians across the generations to understand God the Son in his divine and human natures. In what follows, I will share a handful of quotations outlining this glorious doctrine. You can find these quotations in God the Son Incarnate (pp. 332–38).

Be sure to read these quotations slowly. They are dense, but they will enlarge your adoration for Christ in his unchanging divine nature (cf. Heb. 13:8), even as you celebrate his full humanity and his birth in Bethlehem.

Augustine of Hippo

Christian doctrine does not hold that God took on the flesh, in which He was born of the Virgin, in such wise as to abandon or lose His care of the government of the world, or to transfer this care, reduced and concentrated, so to speak, to that small body.

Cyril of Alexandria

When seen as a babe and wrapped in swaddling clothes, even when still in the bosom of the Virgin who bore him, he [the only-begotten Word of God] filled all creation as God, and was enthroned with him who begot him. For the divine cannot be numbered or measured and does not admit of circumscription. So confessing the Word [to be] hypostatically united, we worship one Son and Lord Jesus Christ, neither putting apart and dividing man and God, as joined with each other by a union of dignity and authority—for this would be an empty phrase and no more—nor speaking of the Word of God separately as Christ, and then separately of him who was of a woman as another Christ, but knowing only one Christ, the Word of God the Father with his own flesh.

Athanasius, On the Incarnation of the Word

For he [Christ] was not, as might be imagined, circumscribed in the body, nor, while present in the body, was he absent elsewhere; nor, while he moved the body, was the universe left void of his working and providence; but, thing most marvelous, Word as he was, so far from being contained by anything, he rather contained all things himself; and just as while present in the whole of creation, he is at once distinct in being from the universe, and present in all things by his own power—giving order to all things, and over all and in all revealing his own providence, and giving life to each thing and all things, including the whole without being included, but being in his own Father alone wholly in every respect—thus, even while present in a human body and himself quickening it, he was, without inconsistency, quickening the universe as well, and was in every process of nature, and was outside the whole, and while known from the body by his works, he was none the less manifest from the working of the universe as well.

John Calvin, Institutes of the Christian Religion

They thrust upon us as something absurd the fact that if the Word of God became flesh, then he was confined within the narrow prison of an earthly body. This is mere impudence! For even if the Word in his immeasurable essence united with the nature of man into one person, we do not imagine that he was confined therein. Here is something marvelous: the Son of God descended from heaven in such a way that, without leaving heaven, he willed to be borne in the virgin’s womb, to go about the earth, and to hang upon the cross; yet he continuously filled the world as he had done from the beginning!

Stephen Wellum, God the Son Incarnate

The extra is the view that, in the incarnation, the Son not only retained his divine attributes but also continued to exercise them in Trinitarian relations. It also insists that, since the Son now, subsists in two natures, he is not completely circumscribed by the limits of his human nature; the Son is able to live a divine life outside (extra) his human nature while simultaneously living a fully human life in his human nature. From the moment of conception, the Son humbled himself. In so doing, he did not override the limitations of his human nature. The Son, in his human nature, lived like we do and accepted the limitations of that nature as our representative, covenant head, and mediator. Yet, in order to account for the incarnate Son’s continual, cosmic exercise of his divine attributes (e.g., Col. 1:17), the church insisted [and should still insist] that the Son’s exercise of his deity is “outside” his human nature and life. (333)

This is the “extra” and it is a glorious, biblical truth we must be careful to hold. To quote John Mayer, that (not-so) great theologian, Christ is “bigger than his body gives him credit for.” For no one else can we say this, but for Christ who is fully and eternally and immutably God, his divine life is not reflected only in his human body.

As we celebrate his birth, therefore, may we not marvel at how Jesus left heaven to come to earth. May we not question if the Son of God knew of his mission to die for sinners. Instead, may our praise take its cue from Scripture. Jesus is son who clung to Mary’s breast and learned the Scriptures from Joseph, his adopted father. But he is at the same time God the eternal son who upholds the universe and receives the praise of heaven.

Truly, this is our God and at Christmas we should take extra care to worship him in his humanity without losing his divinity. Jesus did not lose his divinity when he became a baby, and neither should we when we remember his birth.

Merry Christmas!!

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