This passage (below) is a continuation of the thought of the previous verses (32-41), the emphasis being on alertness. Thus those unbelievers who are living during the time of the tribulation are to be alert and expecting His coming—because He could come at any time. Note that the rapture will have already happened, so that scenario is not in view here. Jesus here is addressing unbelievers, and particularly Jewish unbelievers. In fact, according to Thomas Ice, anytime Jesus uses “you” in this Olivet Discourse, He is referring to Jews—the Jewish remnant. Also, according to John MacArthur, when Jesus says that they are to be “alert,” or “ready,” what is meant is that they are to be saved and thus spiritually prepared to meet Christ as Lord and King–if not, they will meet Him as Judge and Destroyer, for at the time of His return He will destroy all unbelievers and will welcome all believers into His glorious kingdom. Therefore, this passage speaks solely of the second phase of His coming; however, I think we can also apply the lesson of alertness to the unbelievers of today to be ready, thus to be saved, in order to be prepared for His coming in the rapture.
“Therefore be on the alert, for you do not know which day your Lord is coming. 43 “But be sure of this, that if the head of the house had known at what time of the night the thief was coming, he would have been on the alert and would not have allowed his house to be broken into. 44 “For this reason you be ready too; for the Son of Man is coming at an hour when you do not think He will.