“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, the thing that happened at the first Christmas, that the profoundest and most unfathomable depths of the Christian revelation lie. ’The Word was made flesh’ (John 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.”
J. I. Packer, Knowing God (Downers Grove, 1973), pages 45-46.