The meaning of this sentence is a point on which commentators differ widely. An excellent summary of various opinions will be found in Gerhard’s Commentary.
1. Some think that “this generation” means simply “the present generation of men who were living when our Lord was speaking.” This view is a favorite one with many modern Protestants, but it is very unsatisfactory. For one thing, nearly forty years passed away before the prophecy before us was even partially fulfilled by the destruction of Jerusalem. For another thing, it seems a most violent straining of words to say that the destruction of Jerusalem at all fulfilled a very large part of the prophecy before us. The coming of the Son of Man is surely a totally different thing from the taking of a city.
2. Some think that “this generation” means “the heaven and earth,” (as in the following verses,) and the whole frame of creation. This is the view of Maldonatus.
3. Some think that “this generation” means “the whole race of mankind.” This is the view of Jerome and Barradius.
4. Some think that “this generation” means “this order of things,” or dispensation, and that our Lord meant to teach us that the present dispensation was the last one, the “last time” of which St. John speaks. (1 John ii. 18).
5. Some think that “this generation” should have been rendered, “the same generation,” and that it signifies, “the same generation which sees the beginning of the signs of my second advent, will also see the end of them and my personal appearing.” I venture to remark that this rendering would not be the natural sense of the Greek words.
6. Some think that “this generation” means “the faithful, the believers, the company of Christ’s disciples,” and that the general sense is that Christ shall always have a believing people even at the awful tribulations of the time of the end. The elect shall never be destroyed. This is a favorite opinion of the fathers. Origen, Chrysostom, Hilary, Euthymius, and Theophylact all hold it.
7. The soundest and most satisfactory opinion to my mind, is that which makes “this generation” mean the Jewish nation. They had been spoken of by our Lord in this prophecy. Their captivity and scattering had been plainly predicted. The disciples might naturally wonder how such a prediction could be reconciled with the many promises of glory to Israel in the Old Testament prophets. Our Lord answers their thoughts by declaring that this nation, the “Jewish people,” as a separate people, shall not pass away. Though cast down, they were not to be destroyed. Though scattered, they were yet to be gathered again before all things were fulfilled.
Of course the correctness of this view turns entirely on the question whether the Greek word translated “generation,” will bear the sense of “nation,” or “people.” My own belief is, that it will bear the sense, and that it does really bear it in many places of the New Testament. I mention as instances, Matt. xi. 16; xx. 39; xxiii. 36. Luke xi. 50, 51. Acts ii. 40. Philipp. ii. 15. In this last text our translators have actually translated the word “nation.”
I will only add that the view I maintain is held by Mede, Flacius, Ravanellus, Aretius, and Bullinger. Mede’s argument in defence of the view will be found in his works, p. 752, fol. 1672.