What does Luke 17:36 mean?

This verse isn't found in the most reliable manuscripts. In the King James Version it reads, "Two men shall be in the field; the one shall be taken, and the other left." Perhaps the manuscripts that include Luke 17:36 take it from Matthew 24:40. Matthew 24:41 matches Luke 17:35, so a copyist may have thought this sentiment completed a triplet of comparisons. Given the care with which manuscripts were transcribed, it is possible a scribe was reading from a copy of Luke that had Matthew 24:40 written in the margin as a study note and thought it was a correction to the text. Ultimately, it doesn't matter. It is a small deviation with no effect on the truth of God's Word. In fact, the minor amount of such variances, and translators' willingness to point them out, demonstrates the reliability of the biblical manuscripts. In the case of this verse, we know the phrase was said by Jesus at some point, since it is in Matthew's gospel. But it's not likely meant to be repeated in this exact spot in Luke's gospel.

Jesus is explaining that when He returns to earth to bring judgment on those who rebel against God—who reject Him as their Savior—people who are intimately close will wind up on different sides. Two family members who sleep on the same bed could be divided as well as two women who prepare meals together (Luke 17:34–35). Jesus warned His disciples about this earlier, saying His message would create division, even among households—fathers and sons, mothers and daughters, mothers-in-law and daughters-in-law (Luke 12:51–53).

In this case, it's two men who work in the field together. They may be family, or they may be fellow servants or laborers. As with the previous two verses, we don't know what "taken" and "left" signify; it's not clear which is brought to judgment and which is brought to live with Jesus. The point is merely that two people can have very similar lives on earth but vastly different spiritual lives and eternal destinies.