What does "this generation" mean in the verse, "Truly I say to you this generation will not pass away until all these things take place" (Matthew 24:32, Mark 13:30, Luke 21:32)?
Mark's Jesus, after listing all the tribulations that the world must endure before he returns a second time (Mark 13:3-29, see also Matthew 24:3-33) exclaims: "Truly I say to you this generation will not pass away until all these things take place" (Mark 13:30, Matthew 24:34, Luke 21:32). Jesus was directing this remark specifically to his contemporary generation and not to some unknown future generation. Jesus, addressing his disciples "privately" (Mark 13:3, Matthew 24:3) listed what was going to happen before his return. He then added, "Then shall they deliver you up to be afflicted and shall kill you and you shall be hated of all nations for my names sake" (Matthew 24:9). Concerning this, Mark's version adds, "he that shall endure to the end, the same shall be saved" (Mark 13:13). Thus, it appears from this last remark that at least some of the disciples would survive and be present to witness the second coming and the end of time.
According to Mark and Matthew, Jesus expected the tribulation period to occur before the last of his generation died out. Thus, a limit is given within which the prophecies are to be fulfilled. It should be noted that these "tribulations" were not fulfilled in the events of the years 66-73 C.E., the period of the First Jewish-Roman War. Jesus' own statement shows that the culmination of the "tribulation period" was to see the parousia, the second coming of Jesus (Mark 13:26; Matthew 24:3, 30), which certainly did not occur during the war nor subsequently.
All of Jesus' contemporaries died without seeing the fulfillment of his tribulation prophesy. As a result, Jesus' words, especially the expression, "this generation" have undergone reinterpretation. Nevertheless, the translation of genea is "generation" or as Thayer explains it, giving Matthew 24:34 and Mark 13:30 as examples, "the whole multitude of men living at the time . . . used especially of the Jewish race living at one and the same period" (Joseph Henry Thayer, A Greek-English Lexicon of the New Testament, Grand Rapids, Mich.: Zondervan Publishing House, 1979, p. 112). G. Abbott-Smith writes that the Greek word genea means "race, stock, family," but in the New Testament always "generation" (G. Abbott-Smith, Manual Greek Lexicon of the New Testament, 2nd ed., Edinburgh: T.&T. Clarke, 1923, p. 89). Arndt and Gingrich note that the term means "literally, those descended from a common ancestor," but "basically, the sum total of those born at the same time, expanded to include all those living at a given time, generation, contemporaries" (W.F. Arndt and F.W. Gingrich, A Greek-English Lexicon of the New Testament and Other Early Christian Literature, Chicago: University of Chicago Press, 1957, p. 153).
There is no need to interpret the verse, "Truly I say to you this generation will not pass away until all these things take place" otherwise than that Jesus was speaking here of his contemporary generation. The expression "this generation" appears fourteen times in the Gospels and always applies to Jesus' contemporaries. That generation passed away without Jesus returning. Therefore, we are confronted by another unfulfilled promise by Jesus. Jesus did not return during the period he himself specifically designated. Some commentators are of the opinion that "this generation" means the generation alive when this prophecy comes to pass, which they believe has yet to occur. However, the text shows that Jesus was not speaking to an unspecified future generation; he was speaking to his contemporary disciples and directed this prophecy to them personally.