The supreme mystery with which the gospel confronts us… lies not in the Good Friday message of atonement, nor in the Easter message of resurrection, but in the Christmas message of Incarnation. The really staggering Christian claim is that Jesus of Nazareth was God made man — that the second person of the Godhead became the “second man” (1 Cor 15:47), determining human destiny, the second representative head of the race, and that he took humanity without loss of deity, so that Jesus of Nazareth was as truly and fully divine as he was human.

Here are two mysteries for the price of one — the plurality of persons within the unity of God, and the union of Godhead and manhood in the person of Jesus. It is here, in the thing that happened at the first Christmas, that the profoundest and most unfathomable depths of the Christian revelation lie. “The Word became flesh” (Jn 1:14); God became man; the divine Son became a Jew; the Almighty appeared on earth as a helpless human baby, unable to do more than lie and stare and wriggle and make noises, needing to be fed and changed and taught to talk like any other child. And there was no illusion or deception in this: the babyhood of the Son of God was a reality. The more you think about it, the more staggering it gets. Nothing in fiction is so fantastic as is this truth of the Incarnation.

This is the real stumbling block in Christianity. It is here that Jews, Muslims, Unitarians, Jehovah’s Witnesses, and many of those who feel the difficulties concerning the virgin birth, the miracles, the atonement, and the resurrection have come to grief. It is from misbelief, or at least inadequate belief, about the Incarnation that difficulties at other points in the gospel story usually spring. But once the Incarnation is grasped as a reality, these other difficulties dissolve.

If Jesus had been no more than a very remarkable, godly man, the difficulties in believing what the New Testament tells us about his life and work would be truly mountainous. But if Jesus was the same person as the eternal Word, the Father’s agent in creation, “through whom also he made the worlds” (Heb 1:2 RV), it is no wonder if fresh acts of creative power marked his coming into this world, and his life in it, and his exit from it. It is not strange that he, the Author of life, should rise from the dead. If he was truly God the Son, it is much more startling that he should die than that he should rise again.

“’Tis mystery all! The Immortal dies,” wrote Wesley; but there is no comparable mystery in the Immortal’s resurrection. And if the immortal Son of God did really submit to taste death, it is not strange that such a death should have saving significance for a doomed race. Once we grant that Jesus was divine, it becomes unreasonable to find difficulty in any of this; it is all of a piece and hangs together completely. The Incarnation is in itself an unfathomable mystery, but it makes sense of everything else that the New Testament contains.

J.I. Packer, Knowing God, (Inter-Varsity Press), 1993