Gospel in Christmas

Reading through Luke 2 leading up to Christmas I was struck by a common phrase that I've never thought of. An angel comes to shepherds of all people and tells them "fear not I bring you good news". I always understood that as the good news of a baby being born.
            Everywhere else this verb 'bring you good news' is translated as 'preach the gospel' which makes sense, good news is the gospel. But when you read the story again putting in the angel came 'preaching the gospel' it has a different feel, something more connected to a story already being told.
                               

You see the angels came to some shepherds just outside of Bethlehem, the 'city of David'. The great king of Isreal's past started out as a shepherd himself in those same fields. It was there that David began to commune with God and write psalms of praise to him. We aren't given the author of Psalm 148 but the last recorded author is David so it very well could be. This is what was written perhaps a 1,000 years earlier in the same field.

         148 Praise the Lord, praise the Lord from the heavens; praise him in the heights. Praise him, all his angels, praise him, all his hosts.

                           After the angel makes the announcement to some 'random' shepherds a whole hose of angels appears and begin praising God saying.
                                               With the angel a multitude of heavenly hosts praising God and saying glory to God in the highest and on earth peace towards men.

The Gospel of the king who has finally come to rescue men from their sins.