Matthew Poole and continuators on Luke 2:8

8 And there were in the same country shepherds abiding in thefield, keeping watch over their flocks by night.

Bethlehem was a place about which were Pastures for Sheep, as appears from 1 Sam. 17.15. There were Shepherds, abroad in the Night (for so the Word signifyeth) watching over their Flocks, whether the Phrase signifyeth (as some think) successive Watches such as are kept by Souldiers, and by the Priests, I cannot say. This maketh some think, that it is hardly probable, that our Saviour was Born in December in the midst of the Winter, that being no time when Shepherds use in the Night to be keeping their Flocks in the Field.

Marginal references: Or, the night watches.