Wherefore Saint Bernard declared there are here three miracles: that God and man should be joined in this Child; that a mother should remain a virgin; that Mary should have such faith as to believe that this mystery would be accomplished in her. The last is not the least of the three.  The Virgin birth is a mere trifle for God; that God should become man is a greater miracle; but most amazing of all is that this maiden should credit the announcement that she, rather than some other virgin had been chosen to be the mother of God.

Martin Luther, in Martin Luther’s Christmas Book, ed. Roland Bainton (Kindle Locations 133-143).