12:39 Jesus chose another illustration of the importance of preparedness. He compared His return to the coming of a thief in this one. The point is that those whom He visited would not expect His return. This illustration gives a warning whereas the previous one provided encouragement. The previous one presented the possibility of delay, but the present one stresses sudden and unexpected arrival.313
12:40 Jesus concluded by applying the illustrations. By using the title "Son of Man"Jesus may have been implying that the coming of the Son of Man that Daniel had predicted was in view (Dan. 7:13-14). That prophecy dealt with His coming in glory to rule. Elsewhere Jesus said He did not know the time of His return (Matt. 24:36). However, it would be unexpected because the exact day and hour were unknown, and His return would surprise many people (cf. Matt. 24:36, 42, 44; 25:13; Mark 13:32-33, 35).