We have now come down to the last three evil kings of Israel: Pekahiah, Pekah, and Hoshea. The last of these kings became a vassal of King Shalmaneser of Assyria, who then invaded, deported the Israelites and settled other people in their land. The perspective of the author of 2 Kings was that “This occurred because the people of Israel had sinned against the Lord their God…” (2 Kings 17:7)
By contrast, 2 Kings 18-20 focuses on good king Hezekiah of Judah who reigned for twenty-nine years in Jerusalem. 2 Kings offers a more glowing account of Hezekiah than any other king of Judah. “He trusted in the Lord the God of Israel; so that there was no one like him among all the kings of Judah after him, or among those who were before him.” (2 Kings 18:5)
The thing that really set Hezekiah apart was not only that he set about a great reform and return for Judah to wholehearted worship of Yahweh, but that every time he faced potential calamity, he turned to the Lord in prayer. When King Sennacherib of Assyria threatened Judah, “When King Hezekiah heard it, he tore his clothes, covered himself with sackcloth, and went into the house of the Lord.” (2 Kings 19:1) Then, when “Hezekiah received the letter from the hand of the messengers [of Sennacherib] and read it; then Hezekiah went up to the house of the Lord and spread it before the Lord.” (2 Kings 19:14) Each time, that Hezekiah sought the Lord in this way, the Lord sent the prophet Isaiah to encourage him, and the Lord delivered Hezekiah and all of Judah from the King of Assyria.
When Hezekiah became sick and was facing death, Isaiah approached him and told him to set his affairs in order. However, because Hezekiah prayed to the Lord about the matter, the Lord added fifteen years to his life. It was during this extension of life that Hezekiah showed to the envoys of the King of Babylon all the treasures of his house. Isaiah informed Hezekiah afterwards that all of these treasures would indeed be carried away to Babylon one day. However, Hezekiah was not worried about this because he knew it would not happen in his day. This reveals that even a good man can have an improper lack of concern for the future. It should therefore come as no surprise that when Hezekiah “slept with his ancestors,” he had a wicked son, Manasseh, succeed him.
Lawrence Boadt provides this informative summary of developments during Hezekiah’s reign….
At this point, King Hezekiah of Judah…began his own reform sometime between 720 and 700 B. C. Both 2 Kings 18-20 and 2 Chronicles 29-32 stress that he undertook a serious religious renewal against pagan cults very much like that later credited to Josiah. Hezekiah no doubt wanted to bring together the best of the northern tradition and the best of the southern vision of temple and monarchy now that the kingdom of Samaria had been destroyed for good. Most experts believe that it was under Hezekiah that the “J” and the “E” sources were combined to form the Books of Genesis, Exodus, Leviticus and Numbers. There is also some evidence that Hezekiah desired to save older traditions in the label found in the Book of Proverbs (25:1) that “the men of Hezekiah transmitted these proverbs of Solomon.” Possibly then it was under Hezekiah that chapters 5 through 26 (with chapter 28) [of Deuteronomy] were written down as the basis of the reform. When Hezekiah died and his son Manasseh began an age of persecution of true Yahwism and violent rejection of the Deuteronomic program, the book was hidden away in the temple, or simply lost and forgotten in a corner, or still more probably was guarded by the priests and levites until a better moment came. That moment happened under Josiah. The book’s reappearance had a moving effect on the young king, and he followed its program fully.
Hezekiah was also a great builder. The Siloam Inscription dates from the days of Hezekiah and describes the digging of a secure water tunnel from the springs outside the city walls to a pool inside the city. Lawrence Boadt writes, “This was essential if Jerusalem was to withstand the attack of the Assyrian king Sennacherib. It was found in the middle of the tunnel carved into the wall.”
Apparently, Hezekiah was a man who lived by the adage, “Pray as if everything depends upon God and work as if everything depends upon you.”
 Boadt, Reading the Old Testament, 356