Question: "What did Jesus mean when He said, "this generation will not pass"?"
Answer: This quote of Jesus in regards to the end times is found in Matthew 24:34; Mark 13:30; and Luke 21:32. Jesus said, "Truly I say to you, this generation will not pass away until all these things take place." The key to understanding what Jesus means is the context; that is, we must understand the verses that are surrounding verse 34, but especially the verses prior to it. In Matthew 24:4-31, Jesus is speaking of future events. The generation of people living when those events occur is the generation that Jesus speaks of "not passing" until He returns. Jesus had already told those living during His earthly ministry that the kingdom had been taken from them (Matthew 21:43). Therefore, it is imperative that Matthew 24-25 be seen as speaking of a future time. The word “generation” refers to the people alive in the future when the events of Matthew 24-25 will occur.
Another possibility is that Jesus was giving a prophecy with a "double fulfillment." Some of what He was predicting was going to occur during the time of the generation to whom He was speaking. Some of Jesus’ prophecy may have been fulfilled when the Romans destroyed Jerusalem in A.D. 70. However, other aspects of Jesus' prophecy did not occur in A.D. 70; for example, Matthew 24:29-31.The problem with this view is that it does not harmonize with Jesus' statement that "all these things" will take place in "this generation." Therefore, it is best to understand "this generation" as referring to the generation in which the end-times events occur.
Essentially, Jesus is saying that, once the events of the end times begin, they will happen quickly. This concept is echoed in many other Scriptures (Matthew 24:22; Mark 13:20; Revelation 3:11; 22:7,12,20).