The angel said to the shepherds in the field:

    Fear not, for behold, I bring you good news
        of a great joy that will be for all the people.
    For unto you is born this day in the city of David
        a Savior, who is Christ the Lord. (Luke 2:10-11)

Consider what Reformed theologian Karl Barth has written about the birth of our Savior:

In Luke 2:8-14 . . . the angels announce to the shepherds the birth of Jesus at Bethlehem. Once again everything has already happened as fully as possible. "And she brought forth her first-born son, and wrapped him in swaddling clothes, and laid him in a manger, because there was no room for them in the inn."

This is supreme reality, though wrapped in supreme obscurity. There can be no adding to or enriching of it by what transpired in the fields where the shepherds were keeping watch over their flocks by night. What does happen is that the event in the inn is revealed to them in the fields.

An angel of the Lord appears to them. This reminds us already of the divine epiphany at the resurrection--an impression which is confirmed by what follows: "The glory of the Lord shone round about them, and they were sore afraid." As at the transfiguration and in the resurrection appearances, fear is man's first reaction to a mystery surpassing his understanding. But the fear is always temporary, for "perfect love casteth out fear" (1 John 4:18). So the angel says: "Fear not: for behold, I bring you good tidings of great joy, which shall be to all people"--i.e., when it is revealed to the whole people of Israel.

Note that this is a real birth, whether known by few or many, or by these sooner or later. But this birth is made known to the shepherds in the field by God's revelation, and immediately and on the spot it causes them "great joy": "For unto you is born this day in the city of David a Saviour, who is Christ the Lord." This is the revelation of the reality of this birth in the darkness of the night in the field.

The Saviour is there, the Christ is there, the Messiah is there--he has been born! And the word of the angel is not left unsupported. A whole choir of revelation joins in, "a multitude of the heavenly host, praising God and saying . . ."; adoring yet again the reality of this birth; declaring that in the existence of this babe there is irrevocably accomplished the complete triumph of God above and the complete assistance of the men below who are the objects of His goodness: "Glory to God in the highest, and on earth peace among the men of his good pleasure."

It is impossible to exaggerate the importance of the perfect reality of this event if it is to be understood aright. This is what is made known to the shepherds in the field.

Karl Barth, Church Dogmatics, edited by G. W. Bromiley and T. F. Torrance, III/2 (Edinburgh: T. & T. Clark, 1960), pp. 479-480, emphasis added.

Thanks be to God that he has deigned for even us to overhear this good news!