Amen dico vobis quia non praeteribit generatio haec donec omnia haec fiant. Caelum et terra transibunt, verba autem mea non praeteribunt.
Amen I say to you that this generation shall not pass till all these things be done. Heaven and earth shall pass away, but My words shall not pass away.
St. Hilary: Ut autem fides certa esset futurorum, subiungitur “amen dico vobis, quia non praeteribit generatio haec donec omnia fiant”. “Amen” autem dicendo, professionem veritatis adiunxit.

So that faith might be certain of the things to come, there follows after, “Amen I say to you that this generation shall not pass till all these things be done.” By saying “Amen”, he adds a declaration of the truth.
St. John Chrysostom: Haec ergo omnia de fine Hierosolymorum dicta sunt, et quae de pseudoprophetis et pseudochristis et alia omnia quae diximus usque ad Christi adventum futura. Quod autem dixit “generatio haec”, non de ea quae tunc erat dixit, sed de ea quae est fidelium: consuevit enim Scriptura generationem non solum a tempore designare, sed a loco, cultu et conversatione; sicut cum dicitur: “haec est generatio quaerentium dominum”. Ex hoc autem ostendit quod Ierusalem peribit, et amplior pars Iudaeorum destruetur; generationem autem fidelium nulla separabit tentatio.
So all of these things were said about the end of Jerusalem; and those things which were said about false prophets, and anti-christs, and all the other things we noted will come to pass before the return of Christ. Although he said “this generation”, he did not speak of the generation at that time, but about the generation of all the faithful. For Scripture is accustomed to mark a generation not only by time, but by place, religion, and habit of life, as when it is said: “This is the generation of those who seek the Lord.” By this, moreover, he shows that Jerusalem will fall and that the greater part of the Jews will be killed. No trial, however, will split the generation of the faithful.
Origen: Generatio tamen Ecclesiae transibit aliquando totum hoc saeculum, ut haereditet futurum; tamen donec haec omnia fiant, non transibit. Cum autem omnia haec facta fuerint, transibit non solum terra, sed etiam caelum; unde sequitur “caelum et terra”: idest non solum homines quorum vita terrena est, et propterea terra dicuntur; sed etiam illi quorum conversatio est in caelis, et ideo caelum vocantur: transibunt autem ad futura, ut veniant ad meliora.
The generation of the Church will pass away whenever this whole world passes, since it inherits the world to come; however, not till all these things have come to pass will it pass away. Moreover when all these things will have come to pass, not only earth but also heaven will pass away. So follow the words “heaven and earth” that is, not only the men whose life is earthly, and because of whom the earth is so named, but also those whose manner of life is heavenly, and for whom the heaven is named. The latter will cross over to the things to come, as those who are going to better things.
St. Jerome: Hic per generationem omne hominum significat genus, aut specialiter Iudaeorum. Deinde ut magis eos ad fidem praemissorum inducat, subdit “caelum et terra transibunt; verba autem mea non praeteribunt”, ac si dicat: facilius est fixa et immobilia destrui, quam sermonum meorum aliquid decidere.
Here, by “generation” he signifies every race of men, or in particular, the race of the Jews. Then, so that he might draw them the more to confidence in the foregoing prophecies, he adds “heaven and earth shall pass away, but my words will not pass away,” as if to say: it is easier to imagine the destruction of immoveable and unchangeable things than the failure of anything I have said.
(Lest any think that I found those - I hope, interesting - quotations on my own, allow me to introduce you to the Catena Aurea.)
Good work, Iosephe.
Okay, so I was at a Novus Ordo parish when this Gospel was read. The priest said that this is an example of how the Bible isn’t to be read literally. After all, “this generation” — Jesus’ listeners — passed away before this stuff happened, right? He said, “The Baptists down the street take 80% of the Bible literally and the other 20% symbolically. We Catholics reverse the percentages.” Huh? If the literal meaning of “this generation” is “the Christian Church,” then the whole passage — falling celestial bodies and all — can be literal. Or, if the immediate historical reference is a prophecy of the Fall of the Temple in Jerusalem in 70 AD, then the actual physical generation of Our Lord’s day did in fact witness the destruction. In that case, the literal meaning is still true. Of course there is much in the way of moral, allegorical, tropological meanings, etc. But does that mean that the literal meaning can be completely false? Granted this was a parish homily, not a theology class, but it is precisely this sort of simplistic dismissal of the literal meaning that leads the way to dismissing it at more important points: “and God created the heaven and the earth,” “He ascended into Heaven,” “an angel of the Lord appeared unto her, saying . . .”
And then I used to cite to priests (Novus Ordo, again — is there a trend here?) how St. John the Baptist and Our Lord severely chastised the Pharisees and Scribes. They called the latter “hypocrits,” “vipers,” “whitewashed tombs, beautiful on the outside but filled with dead men’s bones,” and “of their father, the devil.” My point had something to do with Extra Ecclesiam Nulla Salus; if this stuff was true of heretics and schismatics in the Old Testament, how much more so in the New Testament. The obfuscatory, mantra-like response from the priest(-s) was “that was midrash, that was how rabbis talked back then.” Well, if this sort of thing is standard midrashic “critique” and not a categorical “dissing” on the order of “anathema sit,” then how precisely *do* you take off the kid gloves? If this stuff about being sons of Satan is all so easily brushed off, what can’t be?
Okay, enough venting.