Scripture spills a lot of ink on Hezekiah and Assyria’s siege of Jerusalem. Isaiah, Kings and Chronicles each devote 1-4 chapters each about it. (2 Kings 17-20; 2 Chronicles 32; Isaiah 36-39). As I read some of them just now I realized part of God’s purpose.
Israel needed to know that the moving of armies and changing of governments was directed by God, not the movers and shakers of the world. They were tempted to fear Assyria instead of God, to trust Babylon or Egypt or their own preparations for disaster (2 Chronicles 32:3-7), instead of trusting God (2 Chronicles 32:8).
Whenever the fragility of the world order becomes obvious, this temptation gets stronger. God gives us this story to remind us that He is in charge, we need not fear, and He will provide for His people.