Teaching in the temple plaza, people raise questions of the Temple and of the end of all things. Like Matthew 24, there are two different conversations being held here. The first is the destruction of the Temple and the city of Jerusalem -- and event that happens in AD 70 under general Titus of Rome. The second event is the second coming of Christ and event we are still anticipating.
In the Temple plaza they are admiring the beautiful temple that King Herod had built. Several critical elements in Jesus predictions. Notice his advice in 20/21. When you see the armies coming, Jesus says to "run away". If you are in Judea you must flee to the mountains and if you are in the city you must get out of town. In the late 60's the Christians remembered this advice from Jesus and when Titus came to quell the Jewish revolt that had begun in AD 66/7. This abandoning of the city of Jerusalem was a key element in the permanent split between the emerging Christian movement and the Jewish religion.
Beginning in 25 we hear of the enigmatic signs of the end. . . the bottom line is pretty simple. Jesus is coming back, we don't know when so be ready. Watch and be alert.