Matthew 24:42

Those of more plain understanding say, that He spoke this of His second coming; but others would say that it applies to an intellectual coming of the word into the understanding of the disciples, for as yet He was not in their understanding as He was to be.

He would have them ever ready, and therefore He says, Watch.

After this again, that they may not ask about it, He added, "Watch therefore, for ye know not what hour your Lord doth come." He said not, "I know not," but, "ye know not." For when He had brought them well nigh to the very hour, and had placed them there, again He deters them from the inquiry, from a desire that they should be striving always. Therefore He saith, "Watch," showing that for the sake of this, He did not tell it. "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. 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.

Having declared that of that hour knoweth no man, but the Father only, He shows that it was not expedient for the Apostles to know, that being ignorant they might live in perpetual expectation of His coming, and thus concluding the whole, He says, Watch therefore, &c. And He does not say, 'Because we know not,' but Because ye know not, showing that He Himself is not ignorant of the day of judgment.

(Ep. 199, 3.) He said this Watch, not to those only who heard Him speak at the time, but to those who came after them, and to us, and to all who shall be after us, until His second coming, for it touches all in a manner. That day comes to each one of us, when it comes to him to go out of the world, such as he shall be judged, and therefore ought every Christian to watch that the Lord's coming may not find him unprepared; and he will be unprepared for the day of His coming, whom the last day of his life shall find unprepared.