A.T. Robertson Commentary Luke 2:8

"And there were shepherds in the same country abiding in the field, and keeping watch by night over their flock." — Luke 2:8 (ASV)

Abiding in the field (αγραυλουντες). From αγρος, field and αυλη, court. The shepherds were making the field their court. Plutarch and Strabo use the word.

Keeping watch (φυλασσοντες φυλακας). Cognate accusative. They were bivouacking by night and it was plainly mild weather. In these very pastures David had fought the lion and the bear to protect the sheep (1 Samuel 17:34f.). The plural here probably means that they watched by turns. The flock may have been meant for the temple sacrifices. There is no way to tell.