Hezekiah was one of ancient Judah's most righteous kings. He was so obedient that 2 Kings, which normally has a dim view of Judah's rulers, says that Hezekiah "trusted in the Lord . . . so that there was none like him among all the kings of Judah after him, nor among those who were before him" (18:5). This is one reason why many Jews today deny that Isaiah 9:1–7 and 11 apply to Jesus. They argue that Hezekiah, whom the Lord used to save Jerusalem (Isa. 36–37), fulfilled the prophet's glorious promises.
This view fails to consider what the Bible as a whole says about Hezekiah. Second Kings, 2 Chronicles, and Isaiah all indicate that while Hezekiah was a godly man in his generation, he was not the anointed Son of David Judah needed. The Chronicler states this explicitly: Hezekiah "did not make return according to the benefit done to him, for his heart was proud. Therefore wrath came upon him and Judah and Jerusalem" (2 Chron. 32:25). God's rescue of Jerusalem from Assyria on account of King Hezekiah was but temporary, for there were not enough righteous people left in the covenant community for the Lord to spare Judah. Hezekiah was not the Messiah, as peace and security were for his days alone. Babylon would finally capture Judah (Isa. 39:5–8).
Incredibly, Hezekiah himself indicates the ongoing failure of God's people to trust the Lord. During Hezekiah's reign, the city-state of Babylon began asserting its independence from Assyria. Eventually, Babylon would replace the Assyrian empire with an empire of its own, but in Hezekiah's day it was a power that was bigger than Judah but smaller than Assyria. It was in Babylon's interest to encourage other powers that resisted Assyria, and this is what it did when it heard of Hezekiah's recovery (Isa. 39).
When Babylonian emissaries arrived at Jerusalem to wish Hezekiah well, Hezekiah could have taken the opportunity to proclaim that his salvation was of the Lord. He could have said that since Judah's trust was in the one true God, Judah was not interested in any partnership with Babylon against their common enemy. Yet Hezekiah did neither, giving the emissaries a view of his treasuries as if to say that Judah would make a fine partner with Babylon. Despite his godliness, Hezekiah still was tempted to trust in other powers against his enemies. And if godly Hezekiah had that problem, how much more was it an issue for the Judahite who was not as faithful as the king?
One commentator notes how Hezekiah's failure shows the importance of a life of obedience. If we trust God only when we are in dire straits, like Hezekiah was with Sennacherib, but forget Him when things are good, then we are treating the Lord like a talisman or good luck charm who helps us when things look down. We are not called to trust the Lord only once at our conversions, but we must seek Him and obey His commandments every day of our lives.