This generation ... - This age; this race of people. A generation is about 30 or 40 years. The destruction of Jerusalem took place about forty years after this was spoken. See the notes at Matthew 16:28.
Till all these things ... - Until these things shall be accomplished. Until events shall take place which shall be a fulfillment of these words, if there were nothing further intended. He does not mean to exclude the reference to the judgment, but to say that the destruction of Jerusalem would be such as to make appropriate the words of the prediction, were there nothing beyond. Compare the notes at Matthew 1:22-23. So when “death” was threatened to Adam, the propriety of the threatening would have been seen, and the threatening would have been fulfilled, had people suffered only temporal death. At the same time the threatening had “a fullness of meaning” that would cover also, and justify, eternal death. Thus the words of Christ describing the destruction of Jerusalem had a fulness of signification that would meet also the events of the judgment, and whose meaning would not be “entirely filled up” until the world was closed.