Albert Barnes Commentary Matthew 24:34

"Verily I say unto you, This generation shall not pass away, till all these things be accomplished." — Matthew 24:34 (ASV)

This generation, etc. This age; this race of men. A generation is about thirty or forty years. The destruction of Jerusalem took place about forty years after this was spoken. (See Barnes on Matthew 16:28).

Till all these things, etc. Until these things shall receive a full accomplishment. Until events shall take place that shall be a complete fulfillment, if there were nothing further intended. He does not mean to exclude here 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.

So when death was threatened to Adam, the propriety of the threatening would have been seen, and the threatening would have been fulfilled, had men suffered only temporal death. At the same time, the threatening had a fullness of meaning that would cover also, and justify, eternal death in hell. Thus the words of Christ, describing the destruction of Jerusalem, had a fullness of signification that would meet also the events of the judgment, and whose meaning would not be filled up until the world was closed.