Previously, I’d cited this verse to explain why it is best to be left behind:

The Son of Man will send his angels, and they will gather out of his kingdom all causes of sin and all law-breakers, and throw them into the fiery furnace. In that place there will be weeping and gnashing of teeth – Matthew 13:41-42

This is what Jesus meant about one being take and one begin left behind in Luke 17:

I tell you, in that night there will be two in one bed. One will be taken and the other left. There will be two women grinding together. One will be taken and the other left. – Luke 17:34-35

The context for the Luke quote is that Jesus is comparing the day when Jerusalem will be sacked in 70 A.D. with the days of Noah (see verse 26) or the days of Lot (see verse 28). The judgement will fall swiftly on that unrighteous city and when it does, the wicked will be swept away but the righteous will be spared.

Another verse comes to mind as well that gets at this point and gives it some historical context:

Therefore I am full of the wrath of the LORD;
I am weary of holding it in.
“Pour it out upon the children in the street,
and upon the gatherings of young men, also;
both husband and wife shall be taken,
the elderly and the very aged…” – Jeremiah 6:11

Jeremiah is warning Jerusalem that just as Israel had been carried away in exile, the same is coming upon Judah. Armies from the north would soon sweep down and carry away the rebellious nation. Likewise, Jesus and the Apostles preached and taught the Jews that the generation Jesus faced had never actually gone into exile, that is, they had never learned what God intended them to learn when he sent them into exile in the first place. There may have been Jews in that day who taught that that they were technically still in exile till the Davidic king, the Messiah, would come and that’s why there was a lot of expectation about the coming of the Messiah in and before Jesus’ day.

But Jesus repeatedly compared the Jews of his day to their fathers who killed the prophets (cf. Matthew 23:29-39). The point is made most strongly when they kill Jesus himself, God incarnate, and yell, “We have no king but Caesar!” (John 19:15) Jesus never compared them to the chastened Jews who waited in exile for their deliverance such as Daniel or Ezekiel. This is why Jesus used the same turn of phrase as Jeremiah. Jeremiah was condemning the god-hating, prophet-killing sinners of his day and Jesus is doing the same. I think Jesus intended that his hearers would make that same connection.

So how do you avoid being “left behind”? You reject Jesus and kill those he sends. That’s how to make sure you are taken but it is to be taken in judgement.