"And there were in the same country shepherds abiding in the field, keeping watch over their flock by night." (Luke 2:8)
In "God's Word for Today", David Fry writes:

The shepherds’ first reaction was fear but it ended with rejoicing. What happened between the moment of fear and their time of rejoicing was their obedience. Of course, one can hardly imagine disobeying such a magnificent manifestation of God’s will. It was not merely hearing the message from the angelic host that persuaded them to seek the Messiah, but also witnessing the great rejoicing of the angels. Soon they too would rejoice. It wasn’t what was happening in the heavens that caused the shepherds to rejoice, but what God was doing on earth, in a manger in Bethlehem. Unlike Mary who kept quiet, the shepherds loudly praised
God for His coming.
The grandeur of Luke 2 is that Caesar Augustus, emperor of one of the greatest empires in history, gave way to a baby in a manger and a moment around which all of history revolves. Caesar had his earthly glory, but Christ received heavenly glory. Ancient rulers sought to be viewed as divine by their subjects, yet the true God became man to be subject to human suffering. Human emperors sought power over humanity; God sought humility among men. The difference is love. The miracle of love is a God who has all power and superiority, yet humbles Himself to become one of us.

Source: Miracles of Jesus, Adult Teacher's Insights, page 18.