Matthew Poole and continuators on Luke 2:9

9 And lo, the angel of the Lord came upon them, and the glory of the Lord shone round about them, and they were sore afraid:

Christ was promised to Men, who by their Occupation were Shepherds, Gen. 47.3. He himself was the Chief Shepherd, and the true Shepherd, Iohn 10.1. The first Publication of his Birth, is made to Shepherds. Not to Shepherds that were idle, but busied in their honest Vocations keeping their Flocks. This Publication of his Birth is made by an Angel, whether the Angel Gabriel before mentioned, or another, is not certain. This Angel, surprizeth the Shepherds, cometh upon them, thinking no such thing, but only minding their business. The Angel comes in a glorious appearance, probably an extraordinary Light, for it is said, it shone round about them, such an appearance of extraordinary Light is, Luke 9.30, 31. That they were sore afraid was but natural, we are naturally affected at suddain and unusual appearances with fear, and amazement.