sabastious...Well, there are two related things under discussion in the passage that one must distinguish: the event itself and the time of the event. The disciples know that the Lord will be coming, which is something that the world as a whole does not know. But even the disciples do not know when the Lord will be coming. The example of the flood was drawn to illustrate this point: "But of that day and hour no one knows, not even the angels of heaven, nor the Son, but the Father only" (v. 36), "Watch therefore, for you do not know on what day your Lord is coming" (v. 42), "Therefore you must be ready, for the Son of Man is coming at an hour you do not expect" (v. 44), "the master of that servant will come on a day when he does not expect him and at an hour he does not know" (v. 50), etc. This is the same theme found in Luke 19:41, which is characteristically Lukan btw and should be distinguished from the texts in Matthew (which do not talk about "the times of the Gentiles" and "the time of your visitation"). The point in present passage is that the time is not knowable even for the elect, and so it will still be a surprise for those expecting it. Those who aren't expecting anything, of course, would be surprised as well. The examples chosen to illustrate this point all vary in how knowable the event itself is. In the case of the parable of the foolish virgins, the arrival of the bridegroom was precisely what the virgins were staying up waiting for; they represent the elect expecting the parousia. In the case of the parable of the faithful and wise servant and the parable of the talents, the servants similarly had a reasonable expectation that their master would return. But in the case of the illustration of the thief coming in the middle of the night, the event itself is not something anyone normally expects when going to bed at night. One may realize it could always be an unlikely possibility, but it is not an event that is expected to happen. The flood is another example of an unexpected event and while it was something that Noah and his family expected, as they prepared for it specifically without knowing when it would occur, the passage makes plain that people in general had no expectation of it. They just carried on with life as usual and knew nothing about it until the event itself came. The main point I'm making is that there is nothing in the passage that says that the people took no note of a warning that Noah had given them (nor is there anything in Genesis about Noah warning them). It simply states that people were ignorant of what was going to happen. It doesn't imply that there were signs preceding the event that one could take the effort to put together to figure out what was going to happen. Similarly in the case of the thief breaking into the house at night, there isn't any advance warning that the break-in is going to happen. It just happens. And even if one knows that it is going to happen, the parable makes plain that the person still wouldn't know when the event would happen, for "if the householder had known in what part of the night the thief was coming, he would have watched and would not have let his house be broken into" (v. 43). As for the parousia, there are to be signs that the event would happen, just like there is with the fig tree (v. 32-33), but that does not mean that the events in the other examples are equally discernable in advance; as mentioned already, there is no advance sign that a break-in will happen. But all these examples are valid examples of the unexpectedness of the time of the event, which is what this portion of the discourse is specifically concerned with.
