Behold, I come as a thief. Blessed is he that watcheth, and keepeth his garments, lest he walk naked, and they see his shame. Revelation 16:15
Alfred Edersheim tells us more concerning the Temple customs that this verse alludes to:
During the night the ‘captain of the temple’ made his rounds. On his approach the guards had to rise and salute him in a particular manner. Any guard found asleep when on duty was beaten, or his garments were set on fire–a punishment, as we know, actually awarded. Hence the admonition to us who, as it were, are here on Temple guard, ‘Blessed is he that watcheth and keepeth his garments’ (Rev. 16:15). But, indeed, there could have been little inclination to sleep within the Temple, even had the deep emotion natural in the circumstances allowed it. True, the chief of the course and ‘the heads of families’ reclined on couches along that part of the [Temple] in which it was lawful to sit down, and the older priests might lie on the floor, having wrapped their priestly garments beside them, while the younger men kept watch.
But then the preparations for the service of the morning required each to be early astir. The priest whose duty it was to superintend the arrangements might any moment knock at the door and demand entrance. He came suddenly and unexpectedly, no one knew when. The Rabbis use almost the very words in which Scripture describes the unexpected coming of the Master (Mark 13:35), when they say, ‘Sometimes he came at the cock-crowing, sometimes a little earlier, sometimes a little later. He came and knocked, and they opened to him. Then said he unto them, 'All ye who have washed, come and cast lots.’
(Mishnah, Tamid. i. 1, 2). (Edersheim, Alfred. 1994. The Temple: Its Ministry and Services. Updated edition. Peabody, MA: Hendrickson Publishers., pg 112)