I read this excerpt from John Piper today...
Now the tremendously important point of this story is seen in the words of Isaiah in Isaiah 37:21-22: "Because you have prayed to Me concerning Sennacharib, King of Assyria, this is the word that the Lord has spoken concerning him."
Because you have prayed! Because you have prayed, 185,000 enemy soldiers lie dead on the plans of Judah.
Think of it! Just think of it. Does prayer win battles?
Hezekiah, because you have prayed, the strongest king in the known world is gone—off the scene of history. Hezekiah, because you have prayed, the witness of my covenant love for David and my zeal for my name has spread throughout the nations.
Because one man prayed.