While Christmas brings tidings of comfort and joy, it also provides one of the most puzzling questions in the Christian faith. The question centers on a simple yet stunning confession in the Gospel of John: “The Word was God. . . . And the Word became flesh” (John 1:1, 14). The term theologians use to describe this miraculous event is incarnation — God the Son became man.

Much about the incarnation bewilders, but perhaps the greatest mystery relates to one word in John 1:14 — became. What does it mean that the Word became? Initially, it seems that God changed. But the Bible says God is unchangeable, or immutable. God declares, “I the Lord do not change” (Malachi 3:6). The psalmist says of God, “You are the same, and your years have no end” (Psalm 102:27). James says that in God “there is no variation or shadow due to change” (James 1:17). How does this fit with John 1:14, “the Word became flesh”?

The incarnation is mysterious, and to deny or ignore its mystery displays some form of hubris. Honest attempts to describe the incarnation will fall short. Nonetheless, God really reveals his ways to us in Scripture. Because God is one, his written word is organically unified. Therefore, we can ask, What must this specific passage mean if everything in Scripture is true? What all of Scripture says about Christ supplies us with concepts and categories that help us interpret John 1:14. We can summarize these concepts and categories in a short sentence: Jesus is one person with two natures.

Two Natures

Jesus has two natures: divine and human. We do not need to venture far from John 1:14 to see this, but a short overview of other passages will help.

“Much about the incarnation bewilders, but perhaps the greatest mystery relates to one word in John 1:14 — ‘became.’”

Jesus is fully God. Harking back to Exodus 3:14, Jesus applies the divine name to himself, saying, “Before Abraham was, I am” (John 8:58). Paul writes, “To [the Israelites] belong the patriarchs, and from their race, according to the flesh, is the Christ, who is God over all” (Romans 9:5). Also a plethora of other texts show Jesus as God (for example, Philippians 2:6; Titus 2:13; 2 Peter 1:1; 1 John 5:20; Hebrews 1:3, 8; Psalm 45:6–7). Additionally, the Bible attributes acts to Jesus that only God performs, like creating (John 1:3), sustaining (Hebrews 1:3), forgiving sins (Mark 2:7), and more. Every attribute belonging to God also belongs to Jesus, because he is God.

Jesus is also fully man. Jesus is “the son of David, the son of Abraham” (Matthew 1:1). Paul says that Jesus “descended from David according to the flesh” (Romans 1:3), that he was “born of woman” (Galatians 4:4), and that he was “born in the likeness of men” (Philippians 2:6–7; also Romans 8:3). Jesus has bones, flesh, and body parts, unlike a spirit (Luke 24:39–43). He “suffered in the flesh” (1 Peter 4:1). He thirsted (John 19:28), ate and drank (Luke 5:30), and slept (Mark 4:38). Thus, the author of Hebrews writes, “He had to be made like his brothers in every respect” (Hebrews 2:17). Every attribute belonging to man belongs to Jesus, except sin (Hebrews 4:15), for he is truly man.

Christ’s two natures are distinct, yet inseparable. In other words, Christ’s two natures are not mixed together to form a third nature, but at the same time, they exist inseparably in the one person of Christ. The Creed of Chalcedon therefore says that Jesus is

to be acknowledged in two natures,
inconfusedly, unchangeably, indivisibly, inseparably;
the distinction of natures
being by no means taken away by the union,
but rather the property of each nature being preserved.

Both divine and human qualities are attributed to Christ, because he has both divine and human natures.

One Person

While Jesus has two distinct natures, he is one person. He is God the Son (John 1:1; Romans 8:3; Galatians 4:4; Hebrews 1:2–5, 8), the second person of the Trinity, the eternally begotten Son of God (John 1:14, 18). In other words, the human nature of Christ did not have its own personhood before being joined to the Son; rather, Christ’s humanity derives its personhood and its very existence from the person of the divine Son. Consequently, if you take the divine Son away from the historical Jesus, there is no historical Jesus. This doesn’t deny Christ’s real humanity; it just describes what sort of humanity Jesus has — a real humanity “personalized” by the divine Son, to use a phrase from Fred Sanders (Jesus in Trinitarian Perspective, 31).

If Jesus is one person with two natures, we inherit a certain grammar — a Christological grammar. Actions belong to persons, not natures; therefore, we attribute Jesus’s actions to his person rather than to either of his natures. But because Jesus’s natures remain distinct, some acts befit one nature rather than the other. To say it the other way around, while some acts befit a specific nature, every act is attributed to Christ’s one person, the divine Son.

This grammar allows us to say, for example, that God the Son died on the cross according to his human nature. Or, as Paul puts it in Acts 20:28, God obtained the church “with his own blood.” Now, according to his divine nature, the Son can neither die nor bleed. But because God the Son has a human nature, and because actions belong to the person rather than the nature, Scripture can speak like this. And we can apply this same logic and grammar to the incarnation.

The Word Became

If Jesus has a human nature, and if change is proper to humanity rather than divinity, then we can attribute change to Jesus’s person according to his human nature. Since Christ’s humanity has no identity or existence apart from the eternal Son uniting it to himself, we attribute the “becoming” of his humanity to the personal subject of the incarnation, the divine Son. So, the divine Son “becomes” not in his divine nature, but according to the coming-into-existence of his human nature.

One might push back since John emphasizes the Word’s becoming, not the flesh’s coming-into-existence. But recall that what is new in John 1:14 is not the Word’s existence, for he eternally existed “in the beginning” (John 1:1). What is new is the Son’s flesh, which is distinct from his divinity. The emphasis on the Word or divine Son in John 1:14 is fitting because the humanity of Jesus exists only in relation to the Son.

Even though the flesh comes into existence, which befits human nature, we attribute this change to the divine Son because it is the Son’s flesh. Yet God the Son does not change because his divine nature is distinct from his human nature. We therefore locate the change in the flesh that comes into existence, an existence wholly dependent upon the act of God, highlighted in Jesus’s virgin birth. In this way, the incarnation does not compromise God’s immutability.

“The divine Son really ‘became,’ yet without change.”

The Son as God does not change, because there is nothing new in the divine nature. What is new is the Son’s flesh, which is distinct from his divine nature. The divine Son really “became,” yet without change, because although in his divine personhood and nature he is immutable, in his human nature he can change. To say it this way is not a contradiction or a cop-out, but another way to confess that Jesus is both God and man.

Incorruptible Joy

The pairing and compatibility of immutability and the incarnation provide Christians with a more solid joy than anything this world has to offer. Without the incarnation, sinners will have no full and lasting happiness, because there is no satisfactory atoning sacrifice. As Athanasius tells us, God the Son “could not die” without human flesh, and so “he assumed a body capable of death” (On the Incarnation, 2; also Hebrews 2:14). Christ’s flesh enables Christ’s sacrificial death, and Christ’s death purchases our joy. He “suffered once for sins . . . that he might bring us to God” (1 Peter 3:18). Christ died to bring us into God’s presence, where “there is fullness of joy” and “pleasures forevermore” (Psalm 16:11).

And since God is immutable, he is incorruptible and immortal (Romans 1:23; 1 Timothy 1:17). Therefore, the object of our joy, unlike the fickle and fading joys of this world, cannot be destroyed. If God is immortal, so also is his glory — meaning our joy in him also is indestructible, for our joy is in an immutable and incorruptible glory. In other words, the incarnation makes joy possible, and God’s immutability ensures that this joy is permanent.