My request is for an examination of the "this generation will not pass away" line in Matthew's "little apocalypse" (Mt. 24:34). Obviously, the most obvious interpretation of this line is false and enemies of the Church often use it to bully believers. My question is: What is the Catholic interpretation?
I've always thought that he must not mean "generation" to mean "the people alive today" but rather something like "the Church". The evidence for this comes right from the text because the next verse ("Heaven and earth will pass away, but my words will never pass away") flows much more easily if it is a rephrasing of the previous point about His movement than if he just suddenly changed the topic to something that would never pass away.
I think this was the point made in Bede's commentary on the subject. But I've heard that the authenticity of that commentary is doubtful.
Still, this has always troubled me. And I wonder if you have a response.I've always found this confusing as well, so I'm glad he asked. It made me read up on it a bit more, and I find it at least somewhat clearer now. By the way, in working through this question, I relied pretty extensively on the massive footnotes in the Navarre Bible. They've really culled a lot of the best commentary from the last two thousand years, allowing even a casual reader to view Scripture through the eyes of some of the great Saints.
The atheist view, which he mentions, is obviously wrong: no one able to describe the Destruction of Jerusalem in such detail (either through Divine foreknowledge, as Christians believe, or con artists writing after the Destruction, as atheists believe) would be unable of knowing whether or not the world ended immediately after. So that can't be what He's saying here. It just doesn't make any sense.
Actually, what makes Matthew 24, as well as the parallel accounts in Mark 13 and Luke 21, so confusing is the Disciples' three-part question. The Disciples were in awe of the Temple, when Christ informs them (this is Mt. 24:2) that "there will not be left here one stone upon another, that will not be thrown down." Then, in the next verse, the Disciples ask, "Tell us, when will this happen, and what sign will there be of your coming, and of the end of the age?" So the Disciples, not Christ, are assuming that the destruction of the Temple will occur at the same time as the Second Coming, and "the end of the age." And Christ is the One who rejects this equation, although He simultaneously uses the destruction of the Temple as a prefigurement of the consummation of the world, comparing and contrasting the two events in ways that make for confusing reading. He weaves His answers about the two events together, so it takes careful reading.
(1) Destruction of the Temple in Jerusalem: 70 A.D.
For example, Christ outlines specific signs of the coming destruction of Jerusalem for them to watch for. In Mark 13:14, He says “But when you see the desolating sacrilege set up where it ought not to be (let the reader understand), then let those who are in Judea flee to the mountains;” with parallel instructions in Matthew 24:15-16. Luke 21:20-22 explains what the warning sign will be for this event: “But when you see Jerusalem surrounded by armies, then know that its desolation has come near. Then let those who are in Judea flee to the mountains, and let those who are inside the city depart, and let not those who are out in the country enter it; for these are days of vengeance, to fulfil all that is written.”
And this happened, exactly as predicted, some forty years later. The desolating sacrilege is predicted in Daniel 9:27, 11:31, and 12:11. It was fulfilled in one since prior to the time of Christ: the Greek ruler Antiochus IV Epiphanes put idols on the Holy Altar in the Temple (see 1 Mac. 1:54). But Christ knows that this was just a foretaste of the humiliation of the Temple, to be fulfilled more fully in 70 A.D., when Nero (whose name in Hebrew numbers 666) ordered the Roman Army headed by his son Titus to crush the Jews. They destroyed the Temple completely, save the Wailing Wall, and then later (under Emperor Hadrian) built a statute of the Roman god Jupiter on the ruins.
When the Roman army assembled and began to encircle Jerusalem, the early Christians remembered Jesus' words. As the Early Church Father (and early Church historian) Eusebius of Caesarea explains: "But the people of the church in Jerusalem had been commanded by a revelation, vouchsafed to approved men there before the war, to leave the city and to dwell in a certain town of Perea called Pella." So Christ gives the Christians a clear signal for when to get ready and go: the signs that a war is about to begin, by the encircling of the army. Instead of doing the logical thing (fortifying themselves in Jerusalem, as something like three million of their countrymen did), the Christians fled to a tiny, unprotected town. So because of Christ's prophesy, not a single Christian is believed to have died during the destruction of Jerusalem.
(2) The End of the World
In contrast to this, Christ outlines a series of events which will occur well before the end (Mt. 24:4-14):
And Jesus answered them, "Take heed that no one leads you astray.So while a war or a rumor of war is the sign that the desolating sacrifice is going to take place, and the Christians should flee Jerusalem, that's not the signal that the End is now. In other words, the Disciples were wrong to think that when the Temple went, so too would the world. Christianity wasn't set up to be reliant upon the Temple, since they have the great High Priest Jesus Christ, and can celebrate the Holy of Holies anytime and anyplace now, through the Eucharist. Jesus then lists a series of horribles that the Church Militant must face: wars, famines, earthquakes, tribulation, martyrdom, apostasy, betrayal, hatred, heresy and schism, wickedness, and lukewarmness. These aren't signs of the end, but simply the beginning. All three Synoptics include this warning (Mt. 24:6-8; Mark 13:8; Luke 21:9). The reason is simple. When we see terrible world events, it's easy to get apocalyptic, and think "It's really the end this time" -- human history is full of these sorts of nay-sayers, in all sorts of religious contexts. But God doesn't work like that. 1 Kings 19:11-13,
For many will come in my name, saying, `I am the Christ,' and they will lead many astray.
And you will hear of wars and rumors of wars; see that you are not alarmed; for this must take place, but the end is not yet.
For nation will rise against nation, and kingdom against kingdom, and there will be famines and earthquakes in various places: all this is but the beginning of the birth-pangs.
"Then they will deliver you up to tribulation, and put you to death; and you will be hated by all nations for my name's sake.
And then many will fall away, and betray one another, and hate one another.
And many false prophets will arise and lead many astray.
And because wickedness is multiplied, most men's love will grow cold. But he who endures to the end will be saved.
And this gospel of the kingdom will be preached throughout the whole world, as a testimony to all nations; and then the end will come.
The LORD said, “Go out and stand on the mountain in the presence of the LORD, for the LORD is about to pass by.”
Then a great and powerful wind tore the mountains apart and shattered the rocks before the LORD, but the LORD was not in the wind. After the wind there was an earthquake, but the LORD was not in the earthquake. After the earthquake came a fire, but the LORD was not in the fire. And after the fire came a gentle whisper. When Elijah heard it, he pulled his cloak over his face and went out and stood at the mouth of the cave.We expect to see God in the massive wind, the earthquake, and the fire, but He comes in the "gentle whisper," instead. Jesus is saying the same thing: don't just assume that because things are catastrophic, that the world is about to end. So He's again separating the End from the Destruction of Jerusalem. One is foretold by war, but the more important one isn't.
And note that after all these calamities, the step before the end is the preaching of the Gospel to the ends of the Earth, an event which wasn't remotely accomplished by 70 A.D., and still remains incomplete. Even here, the gap between preaching to the ends of the earth, and the end of the earth, is separated by a "then," as are all the events. That could mean moments, or millenia, later. The things Christ prophesied came true almost immediately - the early Church was battered and bruised, faced evil from both outside and inside Her walls, and lived in a world torn apart by hatred and violence. This has been true in every century of the Church's existence... and that's Christ's point. It's easy to view the present as the most important time, and to overemphasize the importance of your place in history (World War I was believed at the time to be "the war to end all wars," for example).
The parables and images He uses to describe this all support this. First, He uses the example of the fig tree (Mt 24:32-35), the last of the trees to blossom. During spring, when everything else has come into bloom, the fig tree still hasn't - it doesn't get around to blossoming until "summer is near" (Mt 24:32). So we see all the other signs He spoke of, just as you can go through spring with all of the other trees in bloom... but when will that fig tree ever blossom? Note that the fig tree sign isn't what we're waiting for, per se -- we're waiting for summer -- but the fig tree sign is the very last sign, and it's delayed long after everything else "blooms."
And, of course, Christ is explicit at the end that we won't know the day or the hour (Mt 24:36). The reason is so we'll stay vigilant. If we really knew that the world was going to end on May 21, 2011, we'd plan our lives around it. Sin now, repent in April. But God in His Wisdom has hidden the day and hour our lives will be taken from us. We know we need to be ready at any time to give an account. The Navarre Bible includes this quote: "He wished to hide this from us so that we might remain on our guard and be aware that this might happen to us during our life. He said very clearly that He would come again, but without stating at what moment. Thus, through all generations and at all times His Coming is ardently awaited" (St. Ephrem, Commentarii in Diatessaron, 18, 15-17). They also include this one: "Since we know neither the day nor the hour, we must always be prepared" (St. Athanasisus). These two similar thoughts seem exactly in keeping with Christ's own words in v. 44, where He suggests that precisely because we don't know the day and hour, we need to be vigilant.
(3) The Most Confusing Passage
Finally, let's get to the question proper. The hardest passage to understand is probably Matthew 24:19-36,
 And alas for those who are with child and for those who give suck in those days!  Pray that your flight may not be in winter or on a sabbath.Matthew's recorded this accurately - we see something very similar in Mark 13:17-32 and Luke 21:23-33. In context, Jesus has apparently transitioned from talking about the tribulation of the destruction of Jerusalem to another tribulation entirely, the Great Tribulation, or "the tribulation of those days."
 For then there will be great tribulation, such as has not been from the beginning of the world until now, no, and never will be.
 And if those days had not been shortened, no human being would be saved; but for the sake of the elect those days will be shortened.
 Then if any one says to you, `Lo, here is the Christ!' or `There he is!' do not believe it.
 For false Christs and false prophets will arise and show great signs and wonders, so as to lead astray, if possible, even the elect.
 Lo, I have told you beforehand.
 So, if they say to you, `Lo, he is in the wilderness,' do not go out; if they say, `Lo, he is in the inner rooms,' do not believe it.
 For as the lightning comes from the east and shines as far as the west, so will be the coming of the Son of man.
 Wherever the body is, there the eagles will be gathered together.
"Immediately after the tribulation of those days the sun will be darkened, and the moon will not give its light, and the stars will fall from heaven, and the powers of the heavens will be shaken;
 then will appear the sign of the Son of man in heaven, and then all the tribes of the earth will mourn, and they will see the Son of man coming on the clouds of heaven with power and great glory;
 and he will send out his angels with a loud trumpet call, and they will gather his elect from the four winds, from one end of heaven to the other.
 "From the fig tree learn its lesson: as soon as its branch becomes tender and puts forth its leaves, you know that summer is near.
 So also, when you see all these things, you know that he is near, at the very gates.
 Truly, I say to you, this generation will not pass away till all these things take place.
 Heaven and earth will pass away, but my words will not pass away.
 "But of that day and hour no one knows, not even the angels of heaven, nor the Son, but the Father only.
So what does He mean by "this generation"? There are two possibilities, I think. One is that it's the generation from the sign of the fig tree (see v. 32). Just as within a generation (about forty years in Judaism) from the time of Christ's prophesy, the first tribulation occurred, He seems to be saying that within a generation of the very last sign, the end will come about. That very last sign is apparently "the sign of the Son of man in heaven," which will be followed (we don't know how long after, but apparently soon) by the Second Coming and the Last Judgment. Because so much of the End is intentionally shrouded in mystery, it's hard to say if this is an accurate understanding of the passage.
But there's another understanding as well. Generations often were used as placeholders for dispensations, rather than just counting off a literal geneology. So, in Matthew 1:17, we read: "So all the generations from Abraham to David were fourteen generations, and from David to the deportation to Babylon fourteen generations, and from the deportation to Babylon to the Christ fourteen generations." So He may simply be saying that "this generation," Christ and His Church, will be around until the very end. That would certainly make sense of the next verse. It's popular amongst Evangelical Protestants to inquire as to when "the Church age" will end. Jesus says it won't. This generation won't pass away, because the Church is the Bride of Christ, the full-grown Israel, and because Christ promises as much (Mt. 16:18), and "Heaven and earth will pass away, but My words will not pass away" (Mt. 24:35). This second interpretation strikes me as the correct way of understanding it. It's a reaffirmation of what was prophesied in Daniel 2:44 - an eternal Kingdom, whose members never pass away.