The attack on Jerusalem now takes place, which is also recorded in some depth in 2 Kings and Isaiah. Now it might seem unfair that Hezekiah has done so much good and then gets "rewarded" by this onslaught from the nation of Assyria. However, there is another way to look at it. All the reforms that Hezekiah had made meant that Jerusalem was able to withstand the attack, and the most important reason they were able to see off the Assyrians was that God was for them. If they had continued in their idolatrous ways they would undoubtedly have been defeated. The same applies to our lives. When we walk in faith and obedience we prepare ourselves to withstand anything.
Hezekiah reacted at first by blocking off the supply of water that the besieging army could use. He also built up the defences of Jerusalem. He also encouraged the people to put their trust in the Lord.
We then get a rather condensed account of the siege and defeat of Assyria. The writer of Chronicles is focusing on the how Hezekiah's dedication to the Lord was the determining factor. So Hezekiah was and Jerusalem were saved and the nation was highly regarded by all the nations. There is a clear message here to those who had returned to Jerusalem.
The chapter closes with Hezekiah's downfall. Pride again took hold of a godly man. All of us need to beware of pride, especially when we have enjoyed success. Even so, Hezekiah gets quite a favourable write-up.