This question continues to exercise inquiring minds throughout the centuries, even as the enigmatic figure of the first century Rabbi never ceases to fascinate and capture the human imagination.
This is evidenced in the countless books that were written proposing endless theories about Jesus, not to mention the numerous television documentaries (especially by National Geographic).
The answer that Scripture gives to this question is at once clear and provocative. Jesus Christ is the eternal Word of God who ‘was made flesh, and dwelt among us’, declares John in his Gospel (1:14).
The Apostle Paul says that Jesus is ‘the image of the invisible God, the firstborn of all creation’ (Colossians 1:15). The writer of Hebrews adds: ‘He is the radiance of the glory of God and the exact imprint of his nature’, who upholds the universe by his power (Hebrews 1:3).
Understandably, many people today would reject the truth of the incarnation because it sounds so incredulous to the modern ear. Moderns would have no problems at all with seeing Jesus as an exceptional rabbi, or a nationalistic revolutionary, or even a shaman or mystic.
But even some Christians have found the idea of the incarnation dubious, and questioned if it is altogether necessary for Christianity to continue to perpetuate this claim.
In 1977, the authors of a collection of essays published as The Myth of God Incarnate and edited by the late John Hick controversially called to question the traditional dogma of the incarnation.
In 2005, Hick published The Metaphor of God Incarnate in which he argued that the incarnation must be understood metaphorically and not literally. For Hick, to make the claim that ‘Jesus is the incarnation of God’ is not very different from saying that ‘Winston Churchill incarnated the British will to resist Hitler’.
Liberal Christians like Bishop John Shelby Spong of the Episcopal Church in America reject the incarnation, and insisted that traditional Christology is bankrupt in the modern scientific age.
But the doctrine of the incarnation is not a metaphysical aberration that has somehow infected the early church’s understanding of Jesus Christ, a distortion brought about by Hellenic philosophy. As we have seen, it is clearly found in the New Testament and it has shaped the church’s prayers and liturgy since her inception.
Belief in the incarnation was given creedal form in the Nicene-Constantinopolitan Creed (formulated in the First  and Second Ecumenical Councils ) and the Chalcedonian Creed (451) amidst fierce battles against erroneous concepts of Christ.
In the Nicene Creed, the church maintains that the Jesus who died and rose again is the eternal Son of God, who is of the same essence with God the Father. In the words of the Creed, the incarnate One is ‘the only-begotten Son of God … God of God, Light of Light, very God of very God’.
It is extremely important that we understand what Scripture means when it speaks of the eternal Word ‘becoming’ human flesh. There are at least two erroneous ways of understanding this ‘becoming’.
The first error is to think that in ‘becoming’ flesh, the eternal Word ‘comes into’ an existing human being, Jesus of Nazareth. To think of the incarnation in this way is to fall into the ancient heresy called ‘adoptionism’ (associated with Paul of Samosata). Adoptionism reduces Jesus to merely another prophet in whom the Word of God dwelt.
The second error is to think that in the incarnation there occurred a transmogrification of the eternal Word (Son) into a human being. According to this understanding, at the incarnation the eternal Word ‘changes into’ the man Jesus.
The early theologians of the church were very careful to stress that the incarnation is not just another version of the ‘mythical transformations’ of the gods that we find in some religions. They insisted that since God cannot be subjected to change, in taking on human flesh the second Person of the Trinity did not become other than himself.
Rather, in the incarnation the eternal Son of God takes up human nature without ever ceasing to be God. To put this in another way, in the incarnation the eternal Son does not ‘change into’ a human being, but he ‘puts on’ human nature.
The early Fathers were fond of using the imagery of Aaron donning his high-priestly robe to depict the incarnation. Just as Aaron remained unchanged after assuming his priestly dress, so the Word or Son does not cease to be God when cloaked in human flesh.
Hence, according to the Chalcedonian Definition the Son of God in the incarnation is very God and very Man. The divine and human natures are united in the second Person of the Trinity ‘without confusion, without change, without division, without separation’.
It is also crucial to note that in the incarnation, the eternal Son plunges into the depths of the human condition by taking upon himself post-lapsarian Adamic flesh, i.e., fallen human nature.
Following Hebrews 2:14, Athanasius (296-373) in his great treatise De Incarnatione maintains that in the incarnation the Son ‘takes a body of our own kind’.
As Thomas Weinandy explains, for Athanasius ‘the humanity assumed by the Word was not some generic immunized, sanitized or quarantined humanity, but a humanity taken from the sinful race of Adam …’
As we have seen, the Chalcedonian Definition postulates that the divine and human natures are united in the person of the incarnate Son without confusion, that is, with their integrity intact.
How are we to even begin to understand this with regard to the acts of Jesus of Nazareth? The theologian William Placher suggests that we think of this great mystery in this way.
Because Jesus Christ is God incarnate, he did things that only God can do – he forgave sins, resuscitated the dead, and saved humankind from sin and death. But because Jesus Christ is God incarnate, he took up our human nature and became a man, he did other things that are associated to being human – he ate and drank, he became tired.
And if we ask who was it that did all these things, the answer is: Jesus Christ.