Luke 12:39-40 (NLT)
39 �Understand this: If a homeowner knew exactly when a burglar was coming, he would not permit his house to be broken into. 40 You also must be ready all the time, for the Son of Man will come when least expected.�

Jesus explains to those listening they will not know when He will return, but they should be prepared in case of his return. A homeowner never knows when a burglar might come, but they take preparations to keep safe those treasures which are valuable to them. If they carelessly leave the home unattended it might be that opportunity for the burglar to strike. In the same way if people allow the state of their soul to remain unguarded then when Jesus returns they will be unprepared to go with Him. And for those who have committed themselves to Christ they may find themselves ashamed of their present condition.

English author H. G. Wells, famous for science fiction novels like The Time Machine, The Invisible Man, and The War of the Worlds, once wrote a short story called "The Country of the Blind." It's about an inaccessible, luxurious valley in Ecuador where, due to a strange disease, everyone is blind. After 15 generations of this blindness there was no recollection of sight or color or the outside world at all. Finally a man from the outside�a man who could see�literally fell into their midst. He had fallen off a high cliff and survived, only to stumble into their forgotten country. When he realized that everyone else was blind, he remembered the old adage: "In the country of the blind, the one-eyed man is king." Wells writes: He tried at first on several occasions to tell them of sight. "Look you here, you people," he said. "There are things you do not understand in me." Once or twice one or two of them attended to him; they sat with faces downcast and ears turned intelligently towards him, and he did his best to tell them what it was to see. But they never believed him. They thought he was crazy. The man fell in love with a girl there and the girl's father, Yacob, went to talk to a doctor about him. A conversation ensued: [The doctor said]: "I think I may say with reasonable certainty that, in order to cure him complete, all that we need to do is a simple and easy surgical operation�namely, to remove these irritant bodies [his eyes!]."
"And then he will be sane?" [they asked]. "Then he will be perfectly sane, and a quite admirable citizen." "Thank Heaven for science!" said old Yacob. Wells goes on to point out that the man would not be allowed to marry Yacob's daughter unless he submitted to an operation that would blind him. So what would the man do? Wells writes: He had fully meant to go to a lonely place where the meadows were beautiful with white narcissus, and there remain until the hour of his sacrifice should come, but as he walked he lifted up his eyes and saw the morning, the morning like an angel in golden armour, marching down the steeps�It seemed to him that before this splendour, he and this blind world in the valley, and his love and all, were no more than a pit of sin. And the man who could see escaped the country of the blind with his life. That is where we live�in the country of the blind that is proud of its science, sure of its health, oblivious to the light. It is not only pitiful; it is deadly. Jesus said, "Men love darkness rather than light because their deeds are evil." Jesus had his own name for "the country of the blind." He called it "the world." In his last words to his disciples before going to the cross, Jesus warned them of the hostility they would face�just as he had�in this blind world. Yet rather than pulling his beloved followers out of this blind and hostile world, Jesus sent his own Spirit into his people to convince this world of its blindness. [Lee Eclov, Vernon Hills, Illinois; source:]