Who are the Two Men in the Field? What's this verse about?

The questions we're trying to answer:

1. What event is being depicted?
2. Which man is taken and which is left behind?

Immediate Context

Jesus tells this story in response to a question the disciples asked way back in 24:3: "What will be the sign of your coming and of the end of the age?" Reading the verses immediately preceding 24:40 confirms that Jesus is speaking about "the coming of the Son of Man".

So the answer to Question 1 is: Jesus is describing the Second Coming.

Comparison with the Flood

Jesus tells us in 24:37-39: "For just like the days of Noah were, so the coming of the Son of Man will be. For in those days before the flood, people were eating and drinking, marrying and giving in marriage, until the day Noah entered the ark. And they knew nothing until the flood came and took them all away." Noah's family was carried by the ark, but the wicked people were taken by the waters - to which is the comparison of the man taken in the field being made?

Help from Luke

Luke 17 is another account of Jesus' words. Verses 26 and 27 say, "Just as it was in the days of Noah, so too it will be in the days of the Son of Man. People were eating, they were drinking, they were marrying, they were being given in marriage - right up to the day Noah entered the ark. Then the flood came and destroyed them all." This helps to clarify who is being taken in the field.

So the answer to Question 2 is: The wicked man is taken, the righteous left behind.

This understanding may be confirmed in Luke 17:37. Jesus finished telling the disciples about one being taken and the other left. "The disciples said to him, 'Where, Lord?' He replied to them, 'Where the dead body is, there the vultures will gather.'" However, the question "Where?" may be directed towards the place of judgment rather than the destination of the taken ones. Jesus' response would be indicating that, just as the "when" of the judgment would be obvious, so would the "where". This latter interpretation seems more correct to me.

There may be confirmation that the wicked is taken, in Jesus' conclusion: "Therefore you also must be ready, because the Son of Man will come at an hour when you do not expect him" (v24:44). This is a warning that we should be prepared. Why? Because the unprepared were taken and destroyed in the time of Noah, and the same thing will happen at the Second Coming to those who are unprepared.