What does Luke 19:44 mean?

Jesus is on a donkey, riding into Jerusalem. The crowd around Him chants that the kingdom of David has come (Luke 19:28–40). Instead of celebrating, when Jesus sees Jerusalem, He weeps. He knows the leadership of the Jews will not accept their King and Messiah. They will fail in their responsibility to lead their people to salvation. And so, they will forfeit their city and their temple.

Within forty years of Jesus' earthly ministry, the next generation of Jewish leaders will have a hand in Jerusalem's destruction. There will be so much infighting that when the Roman leader Vespasian finally sees a clear route to take his army to Jerusalem, he waits. Jewish political differences have turned violent, and Vespasian is willing to watch them wear themselves out.

When Vespasian returned to Rome to become emperor, his son Titus followed his father's lead. It's difficult to say what might have happened had the Jewish leaders set aside their differences earlier and fought against Rome together. In the end, the Jews made a valiant effort, and it took the Roman army longer than they expected to take the city. As they finally breeched the eastern wall, the Romans stole the coins and some of the implements in the temple, then set the building on fire. What metal the Romans didn't easily extract melted into the seams of the stone floor. When the soldiers realized it, they tore apart the temple, stone by stone, and scraped the gold and silver from the cracks.

The in-fighting between the Jewish factions probably resulted in many unnecessary deaths. Titus besieged Jerusalem during Passover, one of the three yearly feasts that filled Jerusalem with travelers. When Jews tried to flee Jerusalem and evade the Romans, they were caught and crucified. Some accounts indicate five hundred a day died this way. More than one hundred thousand died of starvation. Over the span of the entire war, nearly as many Jews were captured; the Romans forced some to become gladiators, enslaved many, and burned others alive.

Jesus sees the future: siege works, mass graves, and starving people. Even more, He sees the hundreds of thousands of Jews who will come for the Passover and spend eternity in torment because their leaders will give into envy, refuse to see how He fulfills the prophecy of the Messiah, and lead their people away from their God.