Joy at the birth of a child is not such a unique or surprising thing. Folks since the dawn of time have rejoiced at the birth of their children. It is a universal feeling. So for the angels to have announced "good news of great joy" at the birth of a baby boy in Bethlehem was quite natural. Even Jewish shepherds loved kids back then just as we do, and the shepherds would have been happy one way or another that one of their kin had a child that night. It was for them a "L'chaim" moment, which is the Jewish salute "to life."