He removed the pagan shrines, smashed the sacred pillars, and knocked down the Asherah poles. He broke up the bronze serpent that Moses had made, because the people of Israel had begun to worship it by burning incense to it. The bronze serpent was called Nehushtan.
References for 2 Kings 18:4
Hezekiah trusted in the LORD, the God of Israel. There was never another king like him in the land of Judah, either before or after his time.
He remained faithful to the LORD in everything, and he carefully obeyed all the commands the LORD had given Moses.
So the LORD was with him, and Hezekiah was successful in everything he did. He revolted against the king of Assyria and refused to pay him tribute.
He also conquered the Philistines as far distant as Gaza and its territory, from their smallest outpost to their largest walled city.
During the fourth year of Hezekiah's reign, which was the seventh year of King Hoshea's reign in Israel, King Shalmaneser of Assyria attacked Israel and began a siege on the city of Samaria.
Three years later, during the sixth year of King Hezekiah's reign and the ninth year of King Hoshea's reign in Israel, Samaria fell.
At that time the king of Assyria deported the Israelites to Assyria and put them in colonies in Halah, along the banks of the Habor River in Gozan, and among the cities of the Medes.
For they had refused to listen to the LORD their God. Instead, they had violated his covenant -- all the laws the LORD had given through his servant Moses.
In the fourteenth year of King Hezekiah's reign, King Sennacherib of Assyria came to attack the fortified cities of Judah and conquered them.
King Hezekiah sent this message to the king of Assyria at Lachish: "I have done wrong. I will pay whatever tribute money you demand if you will only go away." The king of Assyria then demanded a settlement of more than eleven tons of silver and about one ton of gold.
References for 2 Kings 18:14