John Chrysostom
He refrained from revealing the time of His return so that His followers would remain vigilant and always prepared. His desire was for them to be constantly eager to encounter Him and to lead lives of righteousness, which is why He indicated that His coming would occur when they least expected it. The essence of His message is this: if individuals were aware of the moment of their death, they would undoubtedly prioritize that moment. Thus, to prevent a sole focus on the day of death, Christ does not specify the day of the universal conclusion nor the moment of each individual's demise, urging that people remain in a state of perpetual anticipation regarding that day; it should be an ongoing concern. He intentionally left the timing of each life’s end undisclosed.
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Moreover, He directly refers to Himself as Lord (Matt. 24:42), a declaration He had not previously made so explicitly. This serves, I believe, as a rebuke to the indifferent, as they do not exhibit the same diligence for their souls as those who remain alert for a thief regarding their possessions. The latter, anticipating the thief's arrival, stay awake and guard their treasures, but you, He asserts, despite knowing that the Lord will undeniably come, remain completely unprepared and neglect to keep watch for the unexpected approach of death; this is the reason that day leads to the downfall of the indifferent. Just as a wealthy man would have taken precautions had he known when he would be robbed, so too would you have fortified yourselves had you been ready.