Watch ye - Be diligent, faithful, and waiting for the return of your Lord, who will come at an unexpected hour.
Master of the house - Denoting here the Lord Jesus.
At even, or at midnight, or - This refers to the four divisions into which the Jews divided the night.

Watch ye therefore - The more the master is expected, the more diligent ought the servants to be in working, watching, and keeping themselves in readiness. Can one who has received the sentence of his death, and has no right to live a moment, need any admonition to prepare to die? Does not a prisoner who expects his deliverance, hold himself in continual readiness to leave his dungeon?

Watch ye therefore,.... Against false Christs, and false prophets; over yourselves, and the whole church; for the words are particularly addressed to the disciples of Christ:
for ye know not when the master of the house cometh; when Christ, of whom the whole family in heaven, and in earth, is named, who is a Son in his own house, is an high priest over the house of God, and Lord of his church and people, whom he has bought with his blood, and provides for with his grace, and by his Spirit, when he will come to break up housekeeping with the Jews, and bring his wrath upon them to the uttermost: whether
at even, or at midnight, or at the cock crowing, or in the morning. This is agreeably to the division of the night among the Jews, who speak of the first watch, the middle of the night, the cock crowing, and morning, as distinct from each other. The three first of these we have in one passage (q):
"every day they remove the ashes from the altar, "at cock crowing", or near it, either before, or after it; and on the day of atonement, "at midnight"; and on the feast days, "at the first watch",''
the same with the evening here: and elsewhere the morning and cock crowing are distinguished (r);
"for a last of the congregation, how long may a man eat and drink? until the pillar of the morning ascends, (or until it is morning,) the words of R. Eliezer ben Jacob; R. Simeon says, until cock crowing.''
And so the phrase, from cock crowing till morning, is used by them (s). The Romans also divided the night in like manner, into evening, the dead of the night, or midnight, cock crowing, and the morning (t). The allusion seems to be to the time of the president of the temple's coming into it, who had the management of the affairs of it, and of appointing to each priest his work: it is said (u),
"whoever would remove the ashes from the altar, rose up early, and washed himself before the president came; but in what hour does the president come? not at all times alike: sometimes he comes, , "at cock crowing", or near it, before it, or after it; and the president comes and knocks for them, and they open to him; and he says unto them, whosoever has washed himself, let him come and cast lots: they cast lots, and he is worthy whom he counts worthy.''
Such who understand these words of Christ's coming by death, or at judgment, apply these seasons to the several ages of men, as childhood, youth, manhood, and old age.
(q) Misn. Yoma, c. 1. sect. 8. T. Bab. Yoma, fol. 20. 9. & Zebachim, c. l. 96. 2. (r) T. Bab. Pesachim, fol. 2. 2. & Taanith, fol. 12. 1. (s) T. Bab. Zebachim, fol. 20. 2. (t) Alex. ab Alex. Genial. Dier. l. 4. c. 20. (u) Misn. Tumid. c. 1. sect. 2.

Watch ye therefore; for ye know not when the master of the house cometh, at even, or at midnight, or at the cock-crowing, or in the morning--an allusion to the four Roman watches of the night.