"Left behind" has become jargon in our culture to describe the fate of those who miss out on the so-called rapture. The concept is taken from Matthew 24:38-41 in which Jesus draws a comparison between the coming of the Son of Man and the days of Noah. He says,
"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, and they were unaware until the flood came and swept them all away, so will be the coming of the Son of Man. Then two men will be in the field; one will be taken and one left. Two women will be grinding at the mill; one will be taken and one left."
The striking thing is that when this passage is considered carefully, it's meaning is quite different from the way it is often understood when taken as a proof-text for rapture theory.
Key to understanding this text is the comparison that Jesus draws between the days of Noah just prior to the flood and the coming of the Son of Man. Jesus begins by describing the attitude of those who go about their usual affairs completely unaware and uninterested in the judgment that God is about to bring upon them in the form of the flood. These folks are eating and drinking, marrying and giving in marriage, and being unprepared for what is coming, they are swept away in judgment when the flood waters come. In this passage, Noah is the only one who is not swept away; he is left safely in the boat while the others are taken away in torrent. Noah is left behind; everyone else is swept away in judgment. We've got to have this straight if we are to understand what Jesus means with what he says next.
Shifting to the coming of the Son of Man, when Jesus speaks of the man and the woman who are "taken" while the others are left, he is comparing those who are taken to those who are swept away in the flood of God's judgment. When Jesus speaks of those who are left, they, like Noah, have been left behind and spared the fate of those swept away in judgment.
Those who want to take this passage as a proof-text for a rapture insist that it is Noah who is taken away safely in his boat as the flood waters come upon those unfortunate folks who are left behind. The weakness of this interpretation is that the grammar of the passage does not support it. Those who are swept away are always spoken of in the plural: they were eating and drinking; they were unaware; they were swept away. Jesus speaks of Noah as a single individual. It is "Noah" (singular) who enters the ark in 24:38 in contrast to "they" (plural) who are swept away in the flood. The antecedent of the prounoun in the plural verb for "they were unaware" (Gk. ouk egnōsan) cannot possibly be the singular individual Noah. It must refer back to those who were eating, drinking, and doing various other things in 24:38.
To sum up, when we carefully consider the grammar of the Noahic context, we see that Jesus is warning his hearers to look for the coming of the Son of Man lest they be taken away in judgment. Those who are left are preserved and saved through that judgment. So, if that's what it means to be "left behind", then sign me up.