"This is what the Lord says to me: 'I will remain quiet and will look on from my dwelling place, like shimmering heat in the sunshine, like a cloud of dew in the heat of harvest.'" NIV translation
We see that God told Isaiah that He would be watching but would not act immediately. As Christians, we can see this in our daily lives as well. Often, God allows us to enjoy our lives as He watches over and protects us without us even knowing it.
"For, before the harvest, when the blossom is gone and the flower becomes a ripening grape, he will cut off the shoots with pruning knives, and cut down and take away the spreading branches. They will all be left to the mountain birds of prey and to the wild animals, the birds will feed on them all summer, the wild animals all winter." NIV translation
Now, we see that God has given His timing for the intervention on behalf of His people. The timing is compared to the harvest of grapes and we see that God will step in just before the time for harvest. We see that the Assyrians will be at the height of their power when God steps in and judges them. This is the same type of thing that happens in Revelation during the last days.
"At that time gifts will be brought to the Lord Almighty from a people tall and smooth skinned, from a people feared far and wide, an aggressive nation of strange speech, whose land is divided by rivers - the gifts will be brought to Mount Zion, the place of the Name of the Lord Almighty." NIV translation
In 2 Chronicles 32:23, we are told that people brought gifts to Hezekiah after the defeat of the Assyrians. In this, we see that God's timing was perfect to accomplish His purpose of drawing men to Him.
The same thing will happen throughout the time of the great tribulation described in Revelation. God will allow the devil to build his kingdom on the earth only to see it quickly destroyed by the very hand of God. This, too, is God calling people to Himself through a demonstration of His power.