Such a note as this could only have been made by Mary herself. She knew her Child was in some mysterious sense the Son of God. A glorious being not of earth had told her that her Boy would be the Savior of Israel. The visit of the rough shepherds to her in the crowded caravanserai, and their strange but quiet and circumstantial story of the angel's visit to them, was only another link in the wondrous chain of events which was day by day influencing her young pure life. She could not as yet grasp it all, perhaps she never did in its mighty gracious fullness; but, as at the first, when Gabriel the angel spoke to her, so at each new phase of her life, she bowed herself in quiet trustful faith, and waited and thought, which perhaps she then showed to Luke or Paul.
The shepherds, however, return to the care of their flocks. They were only made occasional preachers, but it could be argued that they gave a firm and full assent to what had happened to them, and that they were the first fruits of believers under the gospel dispensation. True faith produces great joy and thanksgiving to God, and needs must produce joy, because of the union it maketh betwixt a soul and its desired object.
[From the Pulpit Commentary and Matthew Poole's Commentary]