If we wish to understand the meaning of 'conceived by the Holy Ghost and born of the Virgin Mary', above all we must try to see that these two remarkable pronouncements assert that God of free grace became man, a real man. The eternal Word becomes flesh. This is the miracle of Jesus Christ's existence, this descent of God from above downwards -- the Holy Ghost and the Virgin Mary. This is the mystery of Christmas, of the Incarnation. At this part of the Confession the Catholic Church makes the sign of the Cross. And in the most various settings composers have attempted to reproduce et incarnatus est. This miracle we celebrate annually, when we celebrate Christmas.
If I to grasp this miracle should will,So stands my spirit reverently still.Such in nuce is God's revelation; we can only grasp it, only hear it as the beginning of all things. (Dogmatics in Outline, p. 96).
The question raised by Christmas concerns our willingness to receive a message that God has truly visited this planet. We may not understand the nature of this conception and incarnation. It may go beyond our comprehension of "the facts." But this need not lead to a denial that the incarnation, the visitation of God in the form of a human cannot and did not take place. The further question then is this: if we have been visited by God, how does that message translate into the way we comport ourselves as human beings?