Luke 21:20

“But when you see Jerusalem being surrounded with armies, then know that her desolation is at hand.”

The surrounding of Jerusalem by armies in the future was something constantly referred to in the Old Testament. We can consider, for example, Isaiah 4:4 where it can be assumed and is to happen ‘in that day'; Zechariah 14:2, where in ‘a day of the Lord', ‘I will gather all nations against Jerusalem to battle, and the city will be taken, and the houses rifled, and the women ravished ---; Daniel 9:26, where ‘the people of the coming prince will destroy the city and the sanctuary' (in a context which mentions one who comes on the wing of abomination to make desolate); compare also Joel 3:2. So both Zechariah and Daniel describe such a future event vividly, and an example of what it would be like had been equally vividly portrayed in 2 Chronicles 36:16, where, speaking of the destruction of Jerusalem in around 587 BC, the writer says, ‘until the wrath of the Lord arose against His people, until there was no remedy --- therefore He slew their young men with the sword in the house of their sanctuary ---and they burned down the house of God and broke down the walls of Jerusalem.' There is no difficulty then in seeing the source from which Jesus obtained the vividness of the picture, and like the prophets He is declaring that before the end can come Jerusalem must be destroyed.