What does Luke 21:35 mean?

Jesus is talking to Peter, James, John, and Andrew (Mark 13:3) about how His followers should act considering that we cannot know when He will return (Mark 13:32; Acts 1:6–7). Jesus has already described the events that will herald the event:

"And there will be signs in sun and moon and stars, and on the earth distress of nations in perplexity because of the roaring of the sea and the waves, people fainting with fear and with foreboding of what is coming on the world. For the powers of the heavens will be shaken." (Luke 21:25–26)

Jesus has said that people who live in those days will be able to tell when the day is coming near (Luke 21:29–31). A common reading of the books of Daniel and Revelation reveals Jesus will come at the end of a seven-year tribulation which begins when the Antichrist makes a peace treaty between Israel and their enemies (Daniel 9:24–27). Ideally, it should be simple to tell the time.

However, under that interpretation, the tribulation will occur after the "rapture of the church." This sudden disappearance of millions—or billions—of people will have a catastrophic effect on many nations as well as worldwide communications. Access to Bibles may be limited, especially in areas where the Antichrist has more direct control. Someone who has a Bible may come to Christ but not know when the Antichrist made the treaty. Someone living in "Babylon" may not have any accurate information about end-times events.

Further, the entire world will suffer under the seal, trumpet, and bowl judgments described in Revelation.

Jesus tells His followers to fix their eyes on Jesus' return, not the "cares of this life." Those who, for a while, have the money and power to avoid suffering (Revelation 18:16–19), need to reject wild parties that distract them from coming judgment (Luke 21:34). They need to "stay awake at all times, praying that [they] may have strength to escape all these things that are going to take place, and to stand before the Son of Man" (Luke 21:36).