In Matthew 24:30, Jesus warned the people of Jerusalem that,
They will see the Son of Man coming on the clouds of the sky, with power and great glory.This is often misinterpreted as a description of the second coming. The expression "coming on the clouds" is not a description of the second coming of the Lord. It is a phrase used by the prophets to describe the judgement of a nation. In Isaiah 19:1, the Lord is described as coming on a swift cloud to Egypt. The context makes it clear that this is a description of the collapse of Egypt, and not the second coming. The expression is used in a similar way throughout the Old Testament (Is 13:6; Micah 1:3-5; Ps 97:2,3).
There is a good reason for the similarity of these descriptions to the second coming. Individuals are judged at the second coming, but nations are judged within history. When God has a case against a nation or system, he will bring judgement against it through the events of history. Although the timing is different, both are judged on the same standard, so similar language is used to describe them.
When Jesus speaks of "coming on the clouds" in Matthew 24, he is saying that he will come in judgement against Israel. The Jewish system has been tried and found wanting, so it will be destroyed. There is a confirmation of this interpretation in Matthew 26, where Jesus uses the same expression. He said to the priests, who were trying him,
I say to you all; in the future you will see the Son of Man sitting at the right hand of the Mighty One and coming on the clouds of heaven (Matt 26:64).
The priests did not live to see the second coming of Jesus, but they did see the destruction of Jerusalem and the collapse of the Jewish system. They also saw Jesus being vindicated by the outpouring of the Holy Spirit and the growth of the church. Obviously Jesus was describing these events when he spoke of "coming on the clouds".
Jesus is also referring back to Daniel 7:13,14, where one who comes on the clouds (into the presence of God) is given authority and sovereign power over all nations. His kingdom is everlasting and will never be destroyed. In the interpretation, Daniel is told that this sovereignty will be given to the saints (Dan 7:27).
By quoting Daniel, Jesus was claiming that he would be given sovereignty over the nations. He will rule them from heaven, through his people on earth. The nations will mourn, because they must submit to his power, and acknowledge his glory. They know that if they refuse, they will be destroyed by his judgements. The destruction of Jerusalem was a warning that any nation or system that opposes Christ will eventually be destroyed.