36 “But of that day and hour no one knows, not even the angels of heaven, nor the Son,[a] but the Father only. 37 As were the days of Noah, so will be the coming of the Son of man. 38 For as in those days before the flood they were eating and drinking, marrying and giving in marriage, until the day when Noah entered the ark, 39 and they did not know until the flood came and swept them all away, so will be the coming of the Son of man. 40 Then two men will be in the field; one is taken and one is left. 41 Two women will be grinding at the mill; one is taken and one is left. 42 Watch therefore, for you do not know on what day your Lord is coming. 43 But know this, that 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. 44 Therefore you also must be ready; for the Son of man is coming at an hour you do not expect.The meaning of these verses has been a subject of debate since Luke's gospel adds a possible explanation as to what happens to those who are taken (Luke 17:35-37),
Two women will be grinding grain together; one will be taken and the other left.”whereas Matthew places a similar verse before the section about people being taken or left apparently making the verse refer to "the coming of the Son of man" (verse 28),
“Where, Lord?” they asked. He replied, “Where there is a dead body, there the vultures will gather."
26 “So if anyone tells you, ‘There he is, out in the wilderness,’ do not go out; or, ‘Here he is, in the inner rooms,’ do not believe it. 27 For as lightning that comes from the east is visible even in the west, so will be the coming of the Son of Man. 28 Wherever there is a carcass, there the vultures will gather.Confused?
So was the author of the "Left Behind" series.
I think the key thing for believers to remember is that they have nothing to fear when that time comes and to not waste time worrying about it.