At the heart of Christianity stands an astonishing confession: the eternal Son of God became man.
John states it with remarkable simplicity:
“And the Word was made flesh, and dwelt among us.” — John 1:14
The incarnation of Jesus Christ means that the eternal Son took to Himself a true human nature without ceasing to be God. He did not merely appear human, nor was a human person later elevated into deity. The One who was eternally God became truly man while remaining everything He had eternally been.
Jesus Christ is therefore one person who possesses two complete and distinct natures: a divine nature and a human nature.
The Westminster Confession describes these as “two whole, perfect, and distinct natures” inseparably united in one person, without conversion, composition, or confusion (WCF 8.2).
This truth is essential to the gospel because only such a Savior can reconcile God and man.
The One Who Became Man Is the Eternal Son
The life of Jesus did not begin at Bethlehem.
Before Mary, before Abraham, before Adam, and before creation itself, the Son existed.
John writes:
“In the beginning was the Word, and the Word was with God, and the Word was God.” — John 1:1
The Son is eternal, uncreated, and fully divine. He possesses the same divine nature as the Father and Holy Ghost and is equal with them in power and glory.
All things were created through Him (John 1:3). Before His incarnation He shared glory with the Father “before the world was” (John 17:5). Hebrews says that He upholds all things by the word of His power (Hebrews 1:3).
The child born in Bethlehem was therefore the eternal Creator entering the creation He had made.
The incarnation moves downward from divine glory into human lowliness. A man did not ascend until he became God. God the Son condescended to assume our nature.
What Does the Incarnation Mean?
When John says that “the Word was made flesh,” he does not mean that the divine nature changed into a human nature.
God cannot cease to be God.
The eternal Son assumed humanity. He took a true human nature into personal union with Himself.
What He had always been, He remained. What He had never previously been, He became.
This is why the Westminster Confession uses such careful language. Christ’s two natures are united “without conversion, composition, or confusion” (WCF 8.2).
There is no conversion: deity does not turn into humanity.
There is no composition: pieces of deity and humanity are not blended to create a third kind of nature.
There is no confusion: the properties of the divine and human natures remain distinct.
Christ remains truly God according to His divine nature and truly man according to His human nature.
Yet He is one person.
The historic church calls this the hypostatic union: two complete natures inseparably united in the one person of the Son.
Jesus Possesses a True Human Body and Soul
The Son did not merely acquire a human body.
The Larger Catechism says that He took to Himself “a true body, and a reasonable soul” (WLC 37). Christ assumed complete human nature.
He was conceived and born. He grew physically. He became hungry and thirsty. He grew weary and slept. He experienced sorrow and physical pain.
Luke tells us that “Jesus increased in wisdom and stature” (Luke 2:52). In Gethsemane He said, “My soul is exceeding sorrowful, even unto death” (Matthew 26:38).
His humanity therefore included a genuine human mind, will, affections, body, and soul.
This matters profoundly.
Christ did not save humanity from outside our nature. He entered it.
He became like His brethren so that He might act for them as their representative and serve as their merciful and faithful High Priest.
Conceived by the Holy Ghost and Born of the Virgin Mary
The incarnation took place through the miraculous conception of Christ.
The angel told Mary:
“The Holy Ghost shall come upon thee, and the power of the Highest shall overshadow thee.” — Luke 1:35
Christ received His human nature from Mary through the supernatural operation of the Holy Ghost (WCF 8.2; WLC 37).
The virgin conception establishes both continuity and uniqueness.
Jesus truly belongs to the human race. His humanity is real and derives from His mother.
Yet His entrance into the world is also a unique act of God.
Mary did not give existence to the Son’s divine nature. The Son who was born from her according to His humanity had existed eternally according to His deity.
This is why Matthew identifies Him as Emmanuel: “God with us” (Matthew 1:23).
Jesus Is Truly Human Yet Without Sin
Christ assumed genuine humanity without fallen corruption.
Hebrews says that He “was in all points tempted like as we are, yet without sin” (Hebrews 4:15).
He committed no sinful act, but His sinlessness reaches much deeper than outward conduct.
His thoughts were holy. His desires were pure. His love for His Father was perfect. He loved His neighbor without failure. No original corruption inclined Him toward evil.
This does not make Christ less human.
Sin is not essential to humanity. Adam was genuinely human before he fell, and the glorified saints will remain fully human when every trace of sin has been removed.
Christ reveals humanity as it ought to be.
His temptations were real and brought genuine suffering, but Satan never found an inward ally within Him.
He is the spotless Lamb who can bear the sins of others because He has none of His own.
Two Natures, One Person
The distinction between Christ’s two natures must be preserved without dividing the person.
There are not two Christs.
The divine Son did not enter into partnership with a separate human person. There is one Lord Jesus Christ, and everything Christ does is done by that one person according to the appropriate nature.
This helps explain some striking biblical language.
Paul says that the rulers “crucified the Lord of glory” (1 Corinthians 2:8). The divine nature cannot suffer or die. Yet the person who was crucified according to His human nature is truly the Lord of glory.
Jesus likewise says:
“Before Abraham was, I am.” — John 8:58
According to His humanity, Jesus was born many centuries after Abraham. According to His deity, the person speaking is eternal.
Scripture can therefore speak of the one Christ according to what belongs to either nature because both natures belong inseparably to the same person.
We must neither confuse the natures nor separate Christ into two persons.
The gospel requires the one God-man.
Why Did the Mediator Have to Be Man?
The Westminster Larger Catechism asks this question directly (WLC 39).
Christ had to be man because humanity had sinned and humanity owed obedience to God.
Paul sets Adam and Christ beside one another:
“For as by one man’s disobedience many were made sinners, so by the obedience of one shall many be made righteous.” — Romans 5:19
Christ fulfills in our nature what Adam failed to fulfill.
He was “made under the law” (Galatians 4:4). Throughout His life He rendered the perfect obedience God requires of man.
He also had to be human in order to suffer and die.
God according to His divine nature cannot die. By assuming a mortal human nature, the Son became capable of hunger, weariness, pain, shedding blood, and death.
Our Redeemer therefore belongs genuinely to the race He redeems.
His humanity also makes Him our sympathetic High Priest. He knows bodily weakness, grief, rejection, temptation, pain, and death from within human experience.
“For in that he himself hath suffered being tempted, he is able to succour them that are tempted.” — Hebrews 2:18
The Christian does not pray to a Savior who has observed suffering only from a distance.
Why Did the Mediator Have to Be God?
A merely human mediator could never accomplish our salvation.
WLC 38 explains that the Mediator had to be God so that He could sustain the human nature in the immense work given Him, give infinite worth and efficacy to His obedience and sufferings, satisfy divine justice, conquer His enemies, give His Spirit, and bring His people to everlasting salvation.
The dignity of Christ’s person gives immeasurable worth to His work.
At Calvary, genuine human blood is shed. Yet the person whose blood is shed is the eternal Son of God.
No ordinary man could bear the judicial penalty due to a multitude of sinners and emerge victorious.
No mere creature could conquer death by his own authority, pour out the Holy Ghost upon the church, preserve every believer entrusted to Him, raise the dead at the last day, and bring His people into eternal glory.
Our need is too great for a merely human savior.
The Redeemer must be God.
Why Must He Be God and Man in One Person?
Even deity and humanity alongside one another would not be enough. They must be united in one person.
WLC 40 explains that the Mediator who reconciles God and man must Himself be both God and man in one person so that the works proper to each nature may be received as the work of the whole person.
The One who obeys in human nature is God the Son.
The One who suffers in human nature is God the Son.
The One who rises bodily from the grave is God the Son.
The One who now intercedes for His people in glorified humanity is God the Son.
This personal union gives unity to the whole work of redemption.
Paul therefore writes:
“For there is one God, and one mediator between God and men, the man Christ Jesus.” — 1 Timothy 2:5
Our Mediator truly belongs to both sides of the reconciliation. He possesses the nature of God and the nature of those He came to save.
Christ Our Prophet, Priest, and King
The incarnation equips Christ to fulfill His mediatorial offices of Prophet, Priest, and King.
As our Prophet, Christ reveals God and His will for our salvation. He is Himself the supreme revelation of the Father and continues to teach His church through His Word and Spirit.
As our Priest, He offered Himself once for the sins of His people and now lives to intercede for them. His priesthood requires both His true humanity and the divine dignity of His person.
As our King, He rules and defends His church, conquers His enemies, subdues His people to Himself, and will finally place every enemy beneath His feet.
These offices are not separate from the incarnation. The eternal Son became man in order to fulfill the whole work appointed to Him as Mediator.
The Incarnation Leads to the Cross
Bethlehem must always be understood in the light of Calvary.
Hebrews explains that the Son partook of “flesh and blood” so that through death He might destroy the one who had the power of death (Hebrews 2:14).
He assumed the nature in which obedience was required.
He assumed the nature capable of suffering.
He assumed the nature in which He could die.
Then He “became obedient unto death, even the death of the cross” (Philippians 2:8).
The incarnation is therefore more than a wonder to be admired. It is part of God’s saving purpose.
The Son came in the flesh to redeem sinners through His obedient life, sacrificial death, and victorious resurrection.
The road from Bethlehem leads to Golgotha.
The Incarnate Son Remains God and Man Forever
The incarnation was not temporary.
Christ did not discard His humanity after accomplishing redemption.
He rose bodily. He ascended bodily. He now reigns at the Father’s right hand as the God-man and will return visibly in the same glorified humanity.
WLC 36 therefore says that He “continues to be God and man” in two distinct natures and one person forever.
This is an extraordinary part of Christian hope.
There is a glorified human nature in heaven inseparably united to the eternal Son.
Our Mediator remains our brother.
Our High Priest remains acquainted with our nature.
The hands raised in intercession are the hands that were pierced.
Why the Incarnation Matters
Christianity stands or falls with the identity of Christ.
If Jesus is not truly God, He cannot save with divine power or offer a work possessing the worth necessary for our redemption.
If He is not truly man, He cannot stand in our place, obey in our nature, suffer our penalty, or rise as the firstfruits of redeemed humanity.
If His two natures do not belong to one person, the unity of His mediatorial work collapses.
But the gospel gives us precisely the Savior we need.
He is God enough to save completely and man enough genuinely to represent us.
He possesses divine power and human sympathy.
He is infinitely above us according to His deity and truly one with us according to His humanity.
“God was manifest in the flesh.” — 1 Timothy 3:16
The eternal Son entered our nature without surrendering His deity. He obeyed where Adam failed, suffered in the place of sinners, conquered death, and now reigns in glorified humanity.
And He did it to save.
Westminster references: WCF 8.1–8; WLC 36–42, 44–56; WSC 21–28.