What does he mean by this generation? He means the quality of selfishness, meaning the quality of selfishness will not disappear until all these things have happened.
This generation and this world are connected with the quality of selfishness (when we seek to benefit ourselves with no regard for others). By contrast, the next generation and next world are connected with the quality of bestowal (when we seek to benefit others instead of ourselves).
Here are a few more examples:
- Jesus said, "You are of this world; I am not of this world." (John 8:23, NIV) Meaning, "You are of the quality of selfishness, I am not of the quality of selfishness, I'm of the quality of bestowal."
- Jesus said, "Anyone who loves their life with lose it, while anyone who hates their life in this world will keep it for eternal life." (John 12:25, NIV) Meaning, "...anyone who hates the quality of selfishness will enter into the quality of bestowal for eternity."
- Jesus said, "Now is the time for judgment on this world; now the prince of this world will be driven out." (John 12:31, NIV) Meaning, "Now is the time for judgement on the quality of selfishness, the quality of selfishness will be driven out and replaced with the quality of bestowal."
- Jesus said, "My kingdom is not of this world. (John 18:36, NIV) Meaning, "My kingdom is not of the quality of selfishness, it's of the quality of bestowal."
In everything we do, we should seek to benefit others instead of ourselves.