Why stay awake?

“Beware, keep alert; for you do not know when the time will come. It is like a man going on a journey, when he leaves home and puts his slaves in charge, each with his work, and commands the doorkeeper to be on the watch. Therefore, keep awake—for you do not know when the master of the house will come, in the evening, or at midnight, or at cockcrow, or at dawn, or else he may find you asleep when he comes suddenly. And what I say to you I say to all: Keep awake.”