What does Luke 21:6 mean?
The Mount of Olives is east of Jerusalem (Matthew 24:3). From that height, well above the temple Mount, Jesus' disciples can look down over the porticoes and the temple. They are awed by the majesty of the place where they get to worship God (Luke 21:5). However, Jesus warns that this majesty will not last. Less than forty years later, the Romans will besiege Jerusalem, storm the temple Mount, and set the temple ablaze. The heat will be intense. The gold from the ceremonial implements, the plating on the furnishings, and the coins in the treasury will melt, seeping into the seams of the stones. The soldiers will tear the stones apart so they can scrape the gold away.Having prophesied the events of AD 70, Jesus goes on to lay out long-term hardships which the world will soon find normal: false messiahs, wars, and natural disasters (Luke 21:8–11). Before that, the disciples will be arrested, persecuted, imprisoned, and betrayed by those they are closest to. But they will also experience the intense equipping of the Holy Spirit and share the gospel with kings and governors (Luke 21:12–17).
Jesus' description of the fall of Jerusalem is relatively sedate. It's the city of David and the temple of God, but material things can be rebuilt. He mourns more for the people of Jerusalem who reject Him. When He anticipated His arrival in Jerusalem, He said:
"O Jerusalem, Jerusalem, the city that kills the prophets and stones those who are sent to it! How often would I have gathered your children together as a hen gathers her brood under her wings, and you were not willing! Behold, your house is forsaken. And I tell you, you will not see me until you say, 'Blessed is he who comes in the name of the Lord!'" (Luke 13:34–35)