What does Luke 17:26 mean?

Jesus is describing the conditions of earth before His second coming. The times will compare to those before the flood in an important way: a prevalence of blissful, sinful ignorance. People will be living their lives with no thought to God. They will be "eating and drinking and marrying and being given in marriage" (Luke 17:27)—joyful, celebratory events. They will not understand that judgment is coming.

There are many different interpretations of the "end times:" the final days of human history. Among those views is the idea that Jesus will return to take believers from earth—called "the rapture"—after a seven year period of intense worldwide suffering. The description in this verse is challenging for those who hold to that "post-tribulation" rapture. Under that interpretation, the world will have suffered through seven years of God's wrath, war, and disasters, leading right up to Jesus' return. The timing will be precise as given in Daniel 9:24–27. So, how can people be celebrating, and why would they not know when Jesus is returning?

It's important to remember that Jesus' point here is not to give a description of the tribulation. He's explaining how unexpected His return will be. Even though God warned the people He would destroy them in a specific amount of time (Genesis 6:3), and Noah apparently warned the people as he built the ark (2 Peter 2:5), they did not take the warning to heart or spread the message.

When the political and economic Babylon are in power and the Antichrist is trying to rule the world, the situation will be similar. It's unlikely people in those areas will pay attention to the warnings in a book valued by Christians—who were taken in the rapture—and Jews—whom they are persecuting. Before Jesus' return, Babylon and the Antichrist will make it possible for many people to get extraordinarily rich and lead very decadent lives. They won't be thinking of coming judgment (Revelation 17—18).

Matthew 24:37 uses similar words, although instead of calling it "the days of the Son of Man," Jesus says, "the coming of the Son of Man." It's unclear if the differences are a minor variant or if Jesus warned the disciples more than once.