Mark 13:36

ἐξαίφνης, suddenly, here in Luke 2:13, and four times in Acts. καθεύδοντας : this applies to all the servants, not merely to the porter; therefore all must watch as well as work. In the case of a master absent on a journey, the servants cannot know even the day, not to speak of the hour or watch of the night, as they could in the cases supposed in Luke 12:36; Matthew 25:1. Therefore they must keep awake not merely one night, but many nights, an incongruity which again suggests that we have not here an original utterance of Jesus, but a composite logion with elements borrowed from several parables.