In this chapter, God rescues Jerusalem from the Assyrians.
In the context of the previous chapter, this chapter is straightforward to read and understand. It begins with Hezekiah in distress. He knows that his nation has no strength to resist the Assyrians, so he is counting on the LORD to destroy his enemies. In particular, in 2 Kings 18:32-35, the envoy of Assyria basically says that the LORD is like all the gods of all the other nations that had been destroyed, so the LORD would have no power to resist the Assyrians. Hezekiah hopes that when the LORD hears how he is being slandered, that he would resist the Assyrians. It becomes a question of whether God has the power to defend his name and his reputation against the strength of the Assyrians. The chapter ends with the answer to this question, which is yes (v. 35-37). That's basically the short version of what happens.
This chapter has the first reference to the prophet Isaiah. We have seen many prophets before, but Isaiah is different because he is also a biblical author, the writer of the book of Isaiah. Isaiah is the first "major prophet", which is a term that applies to Isaiah, Jeremiah, Ezekiel and Daniel. They are called major prophets because they wrote longer books, not because they are considered more important than the other prophets (mainly the so-called "minor prophets"). I'm going to talk about Isaiah a LOT more when we get to his book, for now I'm just pointing out Isaiah to my readers because is going to reemerge as one of the most significant authors in the bible and he issues a lot of major prophecies about the coming Messiah. Most of the other prophets throughout the histories (the books of Samuel, Kings and Chronicles) are figures who were important in their time but do not have much significance in later biblical history. In fact, the book of Isaiah itself contains a copy of this story (of Sennacherib's siege of Jerusalem), which is substantially identical to the story in this chapter.
In this chapter, Isaiah is operating very similarly to the other prophets we have seen. He is serving as a representative of the LORD, bearing messages from the LORD to the king in response to the king's prayers and humility. The LORD's response is exactly what we should expect: he is going to drive away the king of Assyria because he wants to demonstrate his supremacy over merely human forces, especially those that would mock him or belittle him. While Hezekiah certainly demonstrates humility here, it is perhaps even more so the pride of the Assyrians that causes God to overthrow them.
Verses 9-13 are interesting because it is after Sennacherib hears a report that the Egyptians are marching out to attack him (Assyria and Egypt clashed frequently) that he sends a second time to the men of Jerusalem threatening them and demanding their surrender.
This time, rather than sending his officials to the prophet, Hezekiah gets even more desperate and goes himself to the temple. This is a great example of why God would choose to honor Hezekiah: in the midst of dire circumstances, his response is to go to the temple in prayer. I'm reminded of 1 Samuel 13:5-9, when Saul was tested. When the enemy gathered at Michmash and his own men were scattering, and the prophet was late, Saul had to decide where his allegiance was going to rest. Was he going to depend on human strength and wisdom or on God? Saul chose human strength and wisdom, and so he perished. In 1 Samuel 30:6, David found himself similarly tested when his wives and children were stolen by Amalekite raiders, his own men were contemplating stoning him, and he had nowhere to turn. Would he depend on his own strength or upon God? David strengthened himself in the LORD his God.
Hezekiah now finds himself in a similar place. The Assyrians are gathering around his walls, Sennacherib is threatening him, and Hezekiah has nowhere to flee, so instead of running away, he goes up: he ascends the temple mount and goes to the LORD for deliverance in his time of need. We saw Ahaz construct an altar to a foreign god when he was in distress (2 Kings 16:10), so Ahaz turned to other gods. Ahaz's son, Hezekiah, turns to the living God for deliverance and boy does he get saved. This time, Isaiah sends a response to Hezekiah even when Hezekiah did not send to Isaiah, and this time the response is in poetic form. Isaiah's response (implicitly referring to Sennacherib) criticizes Sennacherib's pride, when the great king of Assyria sees himself rising above the mountains and drinking the water of foreign lands. Verse 25 tells us that God actually planned for Sennacherib to arise: Sennacherib is a tool in the LORD's hands, and yet in his pride he thinks of himself as the great king and power, greater than the God who made him, and because of that pride he must be brought low.
After Isaiah's prophecy concludes, God promptly answers by killing the Assyrians and later Sennacherib is assassinated by his own sons. As a brief historical sidenote, there are independent historical sources that confirm Sennacherib was, in fact, assassinated by one of his sons, though these sources differ on exactly which son did it. So the majority of this chapter (as it relates to Sennacherib's campaign against Judah and his later death) are historical facts that can be independently verified. Of course, none of the non-biblical sources mention the LORD or the Hebrew God in any way, but I still think it's really cool to have parts of the biblical text so closely mirrored by Assyrian and Babylonian records.