Cyril of Alexandria — as excerpted in the Catena Aurea on Luke 12:35-40

“Our Lord knew the proneness of human infirmity to sin, but because He is merciful, He docs not allow us to despair, but rather has compassion, and gives us repentance as a saving remedy. And therefore He adds, And if he shall come in the second watch, &c. For they who keep watch on the walls of cities, or observe the attacks of the enemy, divide the night into three or four watches.”