Matthew 24:42-51

Watch ye therefore, because ye know not what hour your Lord will come. But know this ye, that if the goodman of the house knew at what hour the thief would come, he would certainly watch, and would not suffer his house to be broken open. Wherefore be you also ready, because at what hour you know not the Son of man will come. Who, thinkest thou, is a faithful and wise servant, whom his lord hath appointed over his family, to give them meat in season.

Blessed is that servant, whom when his lord shall come he shall find so doing. Amen I say to you, he shall place him over all his goods. But if that evil servant shall say in his heart: My lord is long a coming: And shall begin to strike his fellow servants, and shall eat and drink with drunkards: The lord of that servant shall come in a day that he hopeth not, and at an hour that he knoweth not: And shall separate him, and appoint his portion with the hypocrites. There shall be weeping and gnashing of teeth.

Mark 13:33-37

Take ye heed, watch and pray. For ye know not when the time is. Even as a man who going into a far country, left his house; and gave authority to his servants over every work, and commanded the porter to watch. Watch ye therefore, (for you know not when the lord of the house cometh: at even, or at midnight, or at the cockcrowing, or in the morning,) Lest coming on a sudden, he find you sleeping. And what I say to you, I say to all: Watch.

Commentary
by St. John Chrysostom

"But know this, that if the good man of the house had known in what watch the thief would come, he would have watched, and would not have suffered his house to be broken up. Therefore be ye also ready, for in such an hour as ye think not the Son of Man cometh."

For this intent He tells them not, in order that they may watch, that they may be always ready; therefore He saith, When ye look not for it, then He will come, desiring that they should be anxiously waiting, and continually. in virtuous action.

But His meaning is like this: if the common sort of men knew when they were to die, they would surely strive earnestly at that hour.

3. In order therefore that they may strive, not at that hour only, therefore He tells them not either the common hour, or the hour of each, desiring them to be ever looking for this, that they may be always striving. Wherefore He made the end of each man's life also uncertain.

After this, He openly calls Himself Lord, having nowhere spoken so distinctly. But here He seems to me also to put to shame the careless, that not even as much care as they that expect a thief have taken for their money, not even this much do these take for their own soul. For they indeed, when they expect it, watch, and suffer none of the things in their house to be carried off; but ye, although knowing that He will come, and come assuredly, continue not watching, saith He, and ready so as not to be carried away hence unprepared. So that the day cometh unto destruction for them that sleep. For as that man, if he had known, would have escaped, so also ye, if ye be ready, escape free.